Moyes deserves some blame for United's failures, but really, the most blames belongs with Fergie and the club leadership. They are just so mediocre. RVP gave them a boost last season, but now they have been exposed without him they are a completely different team.
Fergie left the cupboard bare. He probably saw the writing on the wall and wanted to leave while he was on top of the league.
Moyes can turn the club around, but it's going to take a couple transfer windows to do that. They really need to work on that midfield.