I'm going to respond to various odds and sods here, so excuse me if this post is a bit disjointed.
Onyx Oblivion said:
Let's look at Blazblue.
http://www.ps3attitude.com/new/2010/08/blazblues-makoto-dlc-worth-8/
It's another fighting game, you may have heard of it.
To expand on the Blazblue point, as I understand it Arc Systemworks actually planned to include the characters as DLC. The fact that at least the two released characters are also fairly large minor characters in the story mode throughout the series also helped. Doesn't mean that they haven't made any effort in it, and should be pretty much be 0% disc-based content.[footnote]I doubt that they would bother re-using the story mode sprites, since there's only about half a dozen of them.[/footnote] (Incidentally, a third character and an SSF4 Arcade Edition style balance patch is coming soon[footnote]Or, at least by "soon" I mean "coming to consoles in Japan at some point next month, and who knows when they will be released in the West". It's entirely possible that we will have the PSP and 3DS port with the balance changes and aforementioned third character released in the West before we see said changes/character in our 360 and PS3 versions; precisely that happened in Japan[/footnote]. Thankfully the balance patch should be free, unlike aforementioned SSF4 Arcade Edition. This is good practice, since it should mean that the balance changes should be observed, unlike potentially in aforementioned SSF4 AE, where the balance changes are optional.)
I suppose the point I want to raise is that if there's a similar counter-argument to be made about pre-announcing DLC and/or expansion packs. For example, Starcraft 2. There will be two expansion packs made for it, and we know this before the game's launch. People are still complaining about how it's still one third of a game. Then again, I suppose there isn't much of the way of a counter-argument largely because this argument is rarely used: Mass Effect got away with doing pretty much the same thing.
Ultimately, the bottom line on the Portal 2 anti-DLC arguments is a question of entitlement. You can argue until you're blue in the face, there's still people (particularly PC gamers[footnote]Railworks is a particularly large punching bag, largely because it's the first Serious Simulator to use a major PC digital distribution system to distribute DLC, and Serious Simulators generate silly amounts of pay-for DLC, usually by third party developers.[/footnote]) who expect all DLC to be free, and since this type of DLC is the sort that you can't just torrent (due to it being intrinsically tied to Steam). I suppose the steep price is also another problem, but then again this is fairly common[footnote]Going back to BlazBlue again: $5/400 MSP for a different announcer? $4/320MSP for a set of four re-colours for each character? And this is perfect sane compared to most of the DLC for your average EA Sports game. A bunch of Madden cheats for $10/800MSP? Take a hike! Not to mention Premium Themes, Gamer Pics and Author Avatars...[/footnote].
And now for something completely different: On to debating the differences between DLC and expansion packs: My definition is that if the content pack can be sold on a disc on its own, then it's an expansion pack. Otherwise, it's DLC. To use an example from ArmA 2, Operation Arrowhead [http://www.amazon.co.uk/ARMA-II-Operation-Arrowhead-DVD/dp/B003QCJY9M/ref=sr_1_2?ie=UTF8&qid=1304192575&sr=8-2] is an expansion pack, while British Armed Forces and Private Military Contractors are both DLC packs, since the two of them are parts of a compilation, Reinforcements [http://www.amazon.co.uk/ARMA-2-Reinforcements-PC-DVD/dp/B004N85CKI/ref=sr_1_3?ie=UTF8&qid=1304192575&sr=8-3]. Another example: Oblivion. Shivering Isles [http://www.amazon.co.uk/Oblivion-Shivering-Isles-PC-DVD/dp/B000NJLQQA/ref=sr_1_6?ie=UTF8&qid=1304192724&sr=8-6] is an expansion pack, while Knights of the Nine [http://www.amazon.co.uk/Oblivion-Knights-Nine-PC-DVD/dp/B000JXPKN0/ref=sr_1_13?ie=UTF8&qid=1304192724&sr=8-13] is DLC, since the disc version comes with seven other bits of DLC.
Ahem. Excuse the wall of text. Before we come to a smaller wall of text known as the footnotes, here's a random song I was listening to while I was making this post.