I think it's down to Federer to be honest.
It's not like he's lost his golden touch but ...i think he doesn't have that raring passion that he did in previous years.
I thought 2005 was an excellent year for him. Can't see this same pattern carrying on.... People can challenge him - not just Nadal!
I can't see Federer going down the rankings. No. But people know what to expect. No doubt Federer has proved to be a mighty player - but it has to slow down one day.
Plus he might want to put a bit more time on home matters!