I believe that Vista represents the functional limits of the MS development processes. Simply put, they don't scale up to this project. Without the untouchable presences of Gates and Ballmer at the helm (any other CEO would have been fired long since), I don't believe they'd have been able to sustain anything like this.
(To be honest, they didn't scale up to NT4, 2000 or XP either, but none of those projects was THIS late and had THIS many features dropped - although the object filesystem was supposed to be in NT4...)