Playing is better than practice, and top players have played just as much if not more than Davydenko; probably more, because they've gone further, and I think Davydenko didn't play as many tournaments last year as he usually does. What is particularly suspicious about it is the sudden and seemingly drastic improvement in his game at an older age, when even great players like Federer aren't as good at 28 as whey were at 26 or 25.
And what, are you saying Davydenko is practicing harder than other top-10 players? Maybe a few, but there's no way he practices more than Nadal, Federer, Djokovic, Murray, Del Potro.
I'm just saying, if we found something out, I wouldn't be totally shocked. Although honestly, he still hasn't done really that much. Although he did just be the #30 at the AO, his first victory over a more highly ranked player.
Depending on how he's playing Verdasco may be a big test for him, although I suspect he'll beat Verdasco as Verdasco's mentally weak.
Then he'll probably face Federer, who I think he is almost as unlikely to beat at a slam as he ever was.