This article is quite packed with logical fallacies, which is quite unusual in your articles Funk.
First: A monthly fee, even if it was only 5 dollars, means you have to fork over your money every single month you may want to play, as the game is only available to you when you feel like forking over for the whole month. In a system like this, the added overtime cost of the game can't be anything short of "infinite" (well, less than that cause you'll die at some point). But considering 15$ a month, every month, that means that I either play the same MMO every month, or buy a brand new game every 3-4 months (depending). That does not mean I can only play 1 game every 3-4 months, that means I can also play a NEW game, along with the old one, every 3-4 months. At the end of the year, I've either spent 180 bucks to play the same game throughout, or I've bought and experienced 3 - 4 games (at 60$ price, which computer games rarely meet, specially if you enjoy the ever so awesome "weekend deals" steam loves to throw around). On the other hand, I shelled out a whooping 35? at the time I bought it for my orange box. It contains 5 games and Team Fortress 2 alone has clocked over 100 hours in-game, and fuck knows how many modding in hammer. I'll most likely still be playing tf2 next year, at which point I will have still spent 35? (it's something absurd like 20$s now) on the whole thing.
Now, correct me if I'm wrong but, you payed money not only for the subscription, every month you've played but ALSO for the copy of the game and every subsequent "expansion". That's an extra game each you could have bought. Meanwhile, a sandbox game like, say, Prototype, would have cost you one game... That's it. You're right, you don't get two years worth of gameplay out of Prototype, but I'd argue every minute you do get is a far more intense and interesting experience than WoW (or assorted MMO-junk)... But since I dislike MMOs, let's not argue the actual quality of the experience (which is crucial mind you) and instead only argue it's length.
Fallout 3 looks like a good candidate. You payed for your game and every other DLC you wanted to have. That's it. I clocked over 100 hours in Fallout 3 without any DLCs, for the whole cost of 1 game. If I wanted, I could go back to it today, right now, turn off this browser and turn it back on, and I would still have payed the exact same 50-something bucks. Meanwhile in WoW you have payed for your game, every subsequent "DLC" and every single month you wanted to just drop in and check on your character.
See, the issue is that the "p2p" is only cheaper on a very specific circumstance: You can't play too much, or too little. If you play too little then you're just paying for idle time with the p2p plan, but the longer you play the more expensive and cost-inefficient it becomes, the exact opposite of "retail games". Then there's also "quality"... And I'd sooner fork over 20 bucks again to play through those 3 hours (1-2 for me at this point) of Portal for the 20th time than I would for an entire month of all MMOs put together.
So no, cost efficient they are not. You can argue that you spend a lot of time in your one game, but I'd say that's a matter of preference more than "efficiency". I like making maps for TF2, ergo I'll most likely spend as much, or more, time on TF2 than you do in WoW. Equally, some people have played Counter Strike Source for something like, 5 hours a day, every day, for 5 years... At the end of the day, the better a game is, and the more you play it, the worse for the costumer the "pay to play" model becomes.