Amid numerous rumors and reports, EGM has confirmed that Microsoft has been paying off large developers to not take their titles to the Playstation 3. Reportedly, Microsoft dropped huge dollars to keep Bioshock from hitting Sony's hands.
timeswasted reports that this comes amongst reports of the same actions taken on games like Stranglehold, Assassin's Creed and many others having their release dates pushed for the PS3 release not because of development issues, but rather because Microsoft has paid to have it that way.
No one knows why Microsoft has gone to such great lengths to keep big titles out of Sony's hands. Only they know the answer, but there is some speculation.
Perhaps the 360 has reached its full potential on current releases.
Bioshock for example is based on the Unreal Engine, a code source that is known for using multiple GPU's and strong processing power. The 360 runs the game beautifully, but based on the hardware, it can definitely do better. The Playstation 3 happens to have a stronger hardware base and it is rumored that running similar code, the PS3 version would be noticeably higher quality.
It will be interesting to see where this goes. And how long has it really been going on? Maybe they just want to completely kill the PS3.