In all fairness there is a potential alternate thought process to Moyes:
Pick someone after Sir Alex that hasn't won anything and has no real experience at this stage, but might surprise everyone by being a real success.
Worst case scenario for a couple of years we don't win anything and he is replaced with a proven manager, who then doesn't have the "burden" of Fergie's success. Someone like Mourinho (or anyone really) will never get much credit for winning as it'll always be worse than Fergie's record. Whereas in a theoretical scenario of a Moyes not winning anything for a few years, a future manager will only be compared to that, rather than Fergie's record.
If Moyes succeeds early on obviously everyone will be over the moon and he will then be able to then build from it.