I think most people's criticisms of Moyes when it comes to strikers is that he likes them to play in a very specific manner in usually a 4-5-1 formation. That's fine if you've got a player like Marcus Bent who will run all day but with players like Saha and Yakubu that just wasn't going to work well for long periods of time, because they're not that kind of player.
Beckford was the one for me, much more than Yakubu where I think there were more factors. He would have been fine as part of a striking pair but by himself he was just lost.
It was no good for either the player of the club to persist with him in a 4-5-1.