This is what's important:
Given the economic situation, nobody wants to start running that tech race again. I think keeping things relatively inexpensive is a good move despite the fact that I think Q4 2010 is a little too soon for the 360's successor.RELEASE & PRICING
Microsoft plans on a Q4 2010 simultaneous worldwide release. The company is targeting a sub $300 price point.
As for the console replacing the PC, it probably won't happen even if they wanted it to. The 90s were full of "entertainment center" electronics and all in one gadgets. None of them ever really set the world on fire. All it ends up doing is shooting the price up scaring away customers who'd buy it for its "main" purpose.
And I wouldn't worry too much about Natal being the exclusive interface. If Nintendo wasn't ballsy enough to try it then MS sure as hell wouldn't be. Now mouse/keyboard support, however, is something I can see being implemented.