That sounds like your supporting his position rather than contradicting it. Why do photographers get favored rewards over sculptors or painters?
Most likely because they're more in demand. But the stuff that pirates are pirating is clearly in demand, they just don't want to pay for it.
Maybe single player games and movies are a special case. RMS avoided the question at the last talk I heard which leads me to believe he doesn't have a good answer.
From an economic perspective, I think it very much is. Even from a technical perspective, I think multiplayer games are (easier to cheat if you have the code, harder to catch you).
On the other hand people will still want to see movies and play games and be willing to pay for those games even copyright were changed so drastically.
I don't think they will. Because, frankly, people are fucking selfish bastards and will take what they can take for free. If it's not in front of them, they will never pay. Exceptions exist, but they are basically noise.
In the case of video games look at ToadyOne and DwarfFortress. He manages to develop DF full time off of donations.
Toady is also one guy, making a game that doesn't require a lot of technical expertise outside of code. I like Tarn a lot and I love DF, and I have donated, but I don't know if you've noticed, he isn't making much at all from his work. Enough to live on, yes--barely. Very barely.
Now expand that to a hundred or two hundred people. You're not getting very far.
If the donations were instead considered to be "investment in finishing the game" then you could see a smaller studio would be able to develop a game, even as grand as HL2, assuming they were "able to stand on the shoulders" of those who came before.
No, you really can't. Hint: the programming is not the largest part of making Half-Life 2. Unless you're positing that we see a bunch of recycled models in every game under the sun, you still have to pay for a legion of 3D modelers. Unless you're positing that we see a bunch of recycled textures in every game under the sun, you still have to pay for a bunch of texture artists. Unless you're positing that we hear the same sounds in every game under the sun, you have to pay for sound artists.
There's a lot more to a game than code. (And frankly, open source hasn't done a very good job of that: all the "big names" are derivatives of the originally closed-source Quake. If you want to see what you get for an open source engine, check out Sauerbraten. Try not to laugh.)