I watched the video on the Xbox Live dashboard a few minutes ago. It only said a few upgrades and that's it. Nothing about CPU's.
The Dashboard is it's own software. They worked on the hardware first, because if they don't, then the software goes nowhere. They probably moved onto the software later on, so they barely changed it. This isn't coming out for a while, right?
... Okay, I actually missed the entire Xbox 360 conference... I caught the "And that's it!" statements on a TV program of it. :( I don't know anything about the new Xbox, but this can all be assumed (what I said), right?