Interesting point of view, though I still disagree with it.
The problem with the logic is that Role-Playing Game means something very specific. It has to do with stats and problems being resolved totally independant of action from the player other than making a desician. The entire thing descended from War Games which was a practice by nerds (typically in college) of fighting historical battles (or battles using historical units) using numbers based on their relative capabilities, to see if they could change the likely outcome by shifting the strategies involved, placement, etc... Things like dice getting involved to represent the role chance could play in the course of a specific event.
War gamers wound up reducing the scale of games, from deciding that they wanted to recreate the entire Battle Of Gettysburg, to say deciding they wanted to conduct a hypothetical encounter between a unit of Yankees and Confederates in terreign of their own device to see who would win. This lead progressively to smaller and smaller skirmishes, until people came up with the idea of confronting a scenario where everyone would control ONE unit instead of a squad or army.
The very first Role-Playing games were nothing but combat simulations involving numbers and dice. No real plot, just an emulation of what would happen if one guy with X equipment and physical traits decided to take a hack at another one. Eventually plots and storylines came into being as people began to create increasingly more sophisticated objectives for people to strive towards.
The idea of the story being the most important aspect of an RPG is actually a fairly recent creation, and arguably the death of RPGs as a lot of arguements on that point seem to largely be intended as an excuse to get away from the mechanics, strategy, and tactics that otherwise defined the genere. Largely because it's relatively easier to design a storyline where characters are lead from point A to point B and the GM keeps things more or less on track, than a framework where characters can literally do anything they want in pursuit of their goals (which might be relatively nebulous, like "Explore The Isle Of Dread to find treasure).
Way back before The Internet was so well travelled I remember how "White Wolf" games got kicked from Fidonet D&D because the attitude they encouraged was not considered to make them true "Role-Playing Games". Things of course changed over time, and I admit so have those games themselves, however I still pretty much subscribe to the logic that there is a differance between a "Roleplaying game" and a "Storytelling game". The focus of the former is for things to be resolved based on the abillities of a character, the focus of the latter is on weaving a narrative and telling a story with a bit of interactivity thrown in. One can have a "Storytelling Game" without needing dice or mechanics at all, as has been demonstrated more than a few times on various web sites, and even so called "statless RPGs" produced over the years. I however maintain that these things are NOT RPGs.
The reason why something like "Pac Man" can never be an RPG is because no matter how you define the story, and what motivations you add, success or failure is based entirely on the abillity of the player to manipulate a joystick in response to the game's stimuli. For it to be an RPG "Pac Man" would have a speed attribute, and the player would just say "Pac Man runs from the ghost" and whether he succeeds or fails is based on Pac Man's speed attribute, and perhaps a die roll to see if maybe something goes wrong (the element of chance, preventing this from becoming a bunch of kids playing army and screaming "I shot you, no I shot you!".
To be honest I increasingly feel that RPGs have a sort of intellectual "nerd cred" attached to them, and a lot of things today want to claim to be RPGs for that reason. The name "RPG" comes along with some assumptions about the abillities of the player, and the depth of the game compared to something which isn't an RPG.
The thing is though that it's all the numbers, desicians, and obscure ways of thinking that made RPGs "smart and nerdy" to begin with. It takes a certain way of thinking to understand a detailed RPG and be able to take pleasure in that kind of indirect control. In comparison simply acting out the roles of characters doesn't require anything really special in terms of thought or understanding. I mean some of the biggest morons in the world have been actors (especially bad ones), and pretty much everyone can get their head around it. At least in the US everyone has had a fantasy about being a big Hollywood star and acting in a movie at some point. Acting well *DOES* take talent, but let's be honest... when it comes to RPGs and such people generally are not acting well, just goofing off like a local school theater guild doing some improv when nobody else is around.
Pretty much everyone can get some entertainment from cinematics, and choosing dialogue options in a Bioware game for example. Not everyone can get entertainment from leveling up skills and modiying equipment to accomplish something. The increasing lack of the latter is what makes something like "Mass Effect 2" far less of an RPG than the first one was, because the quality of the story and voice acting and such has absolutly nothing to do with what makes an RPG what it is. I think a lot of people argue this fact because of "nerd chic" (well certain kinds of nerdism) and people wanting the "cred" as an RPG player so they can be a "1337 gamer nerd" and show how smart they are by talking about how they play RPGs.
See, with real RPGs back in the day, to figure out all the numbers, stats, and charts someone had to be fairly good at reading (and perhaps math depending on the game) just to be able to figure it out. I think people don't realize how things like 1E AD&D were written compared to say the newer editions which are greatly simplified. 1E AD&D pretty much assumed you at least had some college behind you and was written for that crowd just in how it explained things and the choice of words. To play a computer RPG was very simple, a lot of people didn't "get" the numbers and how someone could find entertainment in wandering around in white wire-line mazes in "Wizardry" or whatever, or what "Bob hits the Orc for 6 points of damage" or whatever was all about.
In comparison claiming you play some of the so called "RPGs" today just means you can work a controller/keyboard, and select dialogue options and such from a menu. If you were say 14 and could demonstrate you actually understood 1E AD&D back in the day, that would be a sign you were bright (not a genius, but you needed to have some brains), if today some 14 year old tells me he can play and understand "Mass Effect 2" (getting past the issue of whether he should be playing it due to the "M" rating) I don't think I, or anyone else, is going to be impressed by the requirements there.