Hmm I think first Sony is working on the PS4 right now. So they will be prepared to release their console as soon as MS did it. They made even a survey what the developers want in the PS4 and we had a lot of rumors yet.
Everyones working on their next generation system, but it takes at least a couple of years to move from the page to a product on launch day.
Leaving last generation for this one saved Microsoft a lot of money. In addition to this if they have two consoles they have two chances of getting a sale so their potential market is larger, see PS2 + PS3.
Yep and the PS3 was released just after halfway for the lifecycle of the PS2.
Who knows, you're second guessing their motivations here.
Do you know what its like to live on the far side of Uranus?