I too agree that to say it all comes down to 'who wants it more' is nonsense! I believe it's a mixture of both physical and mental changes......all that hard graft Andy put in, as well as learning to make changes in both his game and his mental attitude! If I was asked to choose just 'one' thing that made the difference between the loss at Wimbledon 2012 and the win in 2013, without taking 'any' of the credit away from Andy, I'd have to say that one thing is Mr. Lendl!
I suppose what people mean when they talk about one player wanting it more is that one just dug that bit deeper when it mattered. Andy certainly did that in the Wimbledon final, to get back into the second and third sets, and he had to do it in that last game. He did it at the USO too, in that fifth set especially. I agree though, it does come down to hard work and physical and mental strength.
I don't quite know about Lendl being the factor between the two Wimbledon finals, although he is a part of it . He was there in the box for both. I do think he played a part in helping Andy see that he did fight against Federer, did play well, and that he should be proud of that, but I also think Andy took a lot from that defeat too, as devastating as it obviously was for him. I think he learned such a lot from it that has helped him so much since.
For me, the thing Andy appears to have done is face up to those major final losses. It seems to me that, perhaps with Lendl's support, he has thought about why he lost those finals, what he could have done differently. Then, it seems to me, that he faced up to the possibility that he might never win a major, might never win Wimbledon. I get a sense somehow that facing those possibilities has released him somehow, if that doesn't sound stupid. It just seems to me that Andy has faced up to those losses and been focused on moving forward.
I think where Lendl has made such a difference is in helping Andy realise that he is good enough to be in the company he is in at the top of the game. He has helped Andy find real belief, which I'm sure has impacted Andy in every way. I've said it before, but even the way Andy moves on the court between points is totally different now, and I'm sure it's because he believes in himself.