Ok if you want a comparison then think of how he was in his goalscoring season compared to how he was when he left. He's never been known for high work rate but he always made the run around the box and he always looked on his toes and alert for a goalscoring opportunity. That's what changed and if he's not doing that then he serves no purpose.
You can say the same about Saha this season and last, too. I read it like the both of them were playing deeper. Saha this season, for example, would go ridiculously deep to get the ball, or drift out wide. I honestly believe he's told to do that by
Moyes. If a player does something
Moyes doesn't want them to do (or doesn't do something he wants them to do) then he changes it -- Moyes doesn't take sh*t, to his credit. So that's my reasoning there I guess.
Yak was a different player to how he was in his first season, you're right. But he did have that injury and that surely effects your game. And when you're going through poor form that does too -- look at Torres. I see him now with Blackburn and he doesn't look like 07/08 Yak to me. He looks like the Yak we had more recently. They're just managing to get goals out of him.
I wish we'd tried to adapt our play to get goals out of him, rather than adapt him (or any striker) to fit into our style. Beckford is a good example as well -- he's obviously a Darren Bent kind of striker (needs a partner of sorts, can't hold the ball up, plays on the last man) but Moyes tried to shape him into a lone striker as that's what our system demands.
Also, as an aside, how often did AJ and Yak play together? That's not rhetorical -- I'm actually wondering!