The Xbox One does not use the same architecture as the 360, the 360 (and PS3) uses the PowerPC architecture which isn't used much any more. The Xbox One and the PS4 both utilize x86 architecture.
The only thing the Xbox One and 360 have in common hardware-wise is use of a smaller secondary cache of RAM that is faster than standard memory.
The Kinect costs around $75 to manufacture and even if they cut the price down $399 for a system that didn't include the Kinect they would be loosing over $20 on every system sold (The Xbox One base system costs more to make than PS4 base system)
Microsoft messed up big time as they are stuck with the system that costs more to make but offers less power than its major competitor (PS4)..