Yeah, so? We already know that people playing FFX1 play along with pc and ps2 gamers. What is your point?
You won't be seeing that with many other games, though, like Halo3 or ut2007 because:
1. Xbox360 can't and won't keep up with the pc mod community of ut2007 and other similar titles. even though you can download other peoples content, after a year of ut2007 being out, almost every room is modded, with a custom map you gotta download in order to play it. Tell me who is going to upload everything from their pc to the xbox with the hassle of upload/download times and non-pc interface. These are pc gamers, proud and loyal. F*** xbox360, they say (generally the hardcore pc gamers of course).
2. Xbox360 relies on XBOX Live. Every game is online enabled and aware of the fact that Clans are supported through xbox live. friends lists are supported through xbox live. and just about everything else. How are you going to play with a pc user on the same level as playing with an xbox360 user? You can't invite the pc user to your clan because he/she is running a pc version, with clans supported through the game (via ps2). This means that pc users will hve to have a pc version of xbox live (already rumored by MS before e3 to solve the pc-xbox360 cross platform problems). Tell me how many Loyal and proud pc gamers are going to pay 60 bucks a month JUST to play games online with xbox360 users when they could play online for free with fellow pc gamers.