Er, I'm a bit confused with totals/exclusives. See, there are 284 games for the X360 and 109 of those are exclusives; this means that the other 175 are multiplatform and will be released on the PS3 too? But there are only 184 announced games on that console so I don't see how tihs adds up.
There are other plattforms than PS3. Lot of the X360 games were launched before the PS3 was out, but you could find versions of the game on PS2 etc..