I can see it having some effect, but mainly for PC people. If I was buying the game at release, then I'd probably pick up the PS3 version and use the "one time use code?" for the Steam version and then just sell the PS3 version. It would be like getting a nice discount on the PC version.
I'd imagine many people (like me) will just wait for when the game goes on sale, like with one of Steam's great Holiday Sales. I picked up Portal 1 awhile back when I bought the Orange Box for $9.99 during a Steam sale. I'll just wait for another one to pick up Portal 2 as well. ;-p
starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 
Skeeuk: "playstation 3 is the ultimate in gaming acceleration"
