They are not all "useless." The sudden change in manager and staff and playing philosophy to an ageing team which has been accustomed to Ferguson's long lasting style has negatively shaken up United. It would have happened with any manager to an extent, maybe not as badly as it did with Moyes. However, saying that David Moyes still is a quality manager and, due to the modern day climate of the game, couldn't afford a slow transition with the team. He built a good top 6 team at Everton with very limited funds and maintained it for +/- 10 years. That shows he has the capabilities to build teams, and without any help whatsoever at United, he struggled to immediatly make his mark, which requires reasonable amounts of time.
He needed another transfer window to replace the players after watching their horror showing the whole season. He wasn't given enough of a chance to build his own team. Not his fault he couldn't add much!
You cannot compare United of this season to its past recent years as there was a complete structural change to the club. Ferguson embodied everything in the club from promoting youth to running a lot of other jobs above that. I am saying that it is not an easy job to replace someone who has been at the club for decades and built the whole environment. Moyes may jave not been the right fit for United but he is still a quality manager who understands the game well and brings integrity to the job on top of that.