It's not so ridiculous, actually. He has adjusted his game perfectly over the years as his career has warranted and while it's true that he is a smudge slower, the adjustments he makes for it do pretty much offset it. And there is no question that his serve is much more of a weapon now. To say it in black and white terminology of "better" is too limiting though. Think of it this way...if he had made no adjustments to his game between about '07 and now, he wouldn't be nearly as effective in '13 as he actually is. So the biggest weapon in the game, the serve...he is better. He has matured in his mental game, preparation, and experience...
It's really not out of the realm. It's also difficult to say do because he is not as dominant now as then, but then the field is much stronger now too, which skews perception.