Valve is the Super Wal-Mart of the game industry.
I don't get your analogy. It would be more appropriate to say that Valve is to digital distribution as Microsoft is to operating systems. Wal-Mart has plenty of viable competitors.
Steam isn't needed to distribute content digitally, nor is any standardized platform.
But it's more convenient for both the consumer and the seller. Besides, for
years Steam was exclusively for Valve games. Then they branched out and let other companies sell their games through Steam. During that time, other companies had plenty of opportunities to build their own digital distribution platform, but they didn't. They flocked to Steam. That was their choice, and they chose to make a standard out of Steam. Stop using Windows all together if you're against this sort of thing, because it's exactly the same story.
Well, for one, I think it would do justice to say Valve STARTED the realism plague. They basically created the stardard model for a next-gen FPS with HL2.
That's about as sound as blaming ID Software for the mere existence of the FPS genre. For a while after the first Doom came out, all first-person shooters were called "Doom clones".
If Valve didn't do it, someone else would have had the ingenuity to do it eventually, anyway. You can't blame the creative people who did it first. Companies observe a product's success and think, "Well if I do that too, then I could be just as successful as they are!" You see this all the time in television, film, toys -- you name it. But you don't blame who did it first. Ever. Because that's just promoting a total lack of ingenuity.
Edit: Ugh it's late/early and I'm tired. That argument probably isn't even on the right topic.