Your GM doesn't have to be a new blood to rebuild because Scott Pioli is killing it in KC right now. But I think your HC typically does because they need to totally defer to the GM on personnel matters. Seasoned coaches command more say and having a headcoach in charge of personnel doesn't work.
As for Bill Belicheck, he's not really a retread in the same way MS is. He only coached the Browns for four seasons and didn't make his name with that organization before he became the coach of the Patriots. He's a Patriot. MS is a repurposed Denver Bronco, i.e. retread.
Our roster got older last season under this new regime. That's not symptomatic of an actual rebuild. The young turnover we're generating is mostly end of the roster types rather than excellent young drafted starters, and we still don't have a sensible plan at QB. If this is us rebuilding then it's going to take a long time to complete because we're still relying on older players (FAs and UDFAS) to fill most of our new positions. The FA moves we make now won't make it through the development of a drafted QB in 2012 or later.In my opinion Mike and Bruce are currently rebuilding the redskins. Turnover of our roster in the last year and several months has been significant. The Donovan McNabb move doesn't go inline with a full rebuild, but pretty much everything else they've done has.
What TB, KC, Detroit, St. Louis, and SF are doing is a true rebuild and that's what I want us to do when I say we need to rebuild.