I'm predicting longer legs for the 360 version, that's all. More than likely, the gamers who are picking up Orange Box and PGR4 now will simply pick up FIFA/PES at a later date, because it will still be available.
The attach rate for the PS3 version would have to be much higher for it to outsell the 360 version in every country (at least where the 360 still has an LTD lead), if FIFA and PES are the only desirable PS3 games at the moment obviously their attach rates would be higher at the start. It's quite obvious that if Halo didn't release the same week as FIFA, FIFA would've been the best-selling 360 game that week and in subsequent weeks, and would've garnered additional sales.
Look at the Madden sales from August to September NPD...The 360 version outsold the PS2 version over the first few weeks of release by several hundred thousand, but in September it was outsold by the PS2 version, which is probably due to the PS2 having a larger userbase with more casual gamers, but also due to Halo sucking up a big chunk of retail dollars.