For what it's worth, I don't think it is the appointment of Moyes that has put United he would this predicament, but Moyes deciding he wanted to bring his own back room staff and removing the old guard that, had served them for so well, in many cases, for so many years. I think it's hard to imagine what a transition that is and, to some degree, is what we've done well for the transition from Mancini to Pellegrini.
Structure is just as important as the individual in the process of change management - keeping the likes of Vieira, albeit in a different role, and Kidd in place have, one can only presume, helped the transition for Pellegrini no end as it helps integrate his own ideas and makes it far easier when bringing in Cousillas and Mancisidor, i.e. there's enough change to accurately reflect the change in leadership but not enough to upset the apple cart. Now compare that to United who, for reasons unknown, have given a relatively unproven, in terms of success on the biggest platform, manger with a reputation amongst Everton fans for 'bottling' it see Villarreal, FA Cup final defeat, defeat to Wigan in last season's cup and umpteen others where Everton missed their big chance a free hand in bringing in his own backroom staff.
This screams to me that Moyes either i) believes they're a better coaching set-up than what was in place under Ferguson or ii), which I think is much more likely, that Moyes does not have a personality strong enough to have replaced Ferguson and kept Ferguson's coaching staff in place. It's easy to say with hindsight, but this decision should have set all kinds of alarm bells off at United when Moyes requested to bring his own coaching staff with him - without looking it up, I think he's only kept Joyce and let the others go - OK, Moyes is undoubtedly at fault for making this change but who at United, when discussing the terms of Moyes' move said "Yeah, that's a cracking idea Davey, I'm sure Phil Neville and Steve Round will take Cleverley and Chris Smalling to the next level"?
This, for me, points to that inherently and frequently incoherent Glaswegian piss head setting up Moyes for a fall, all to protect his own legacy.