Well, as said, he almost always does this I think.
he always plays Auckland (and won there last two years)
what's new is playing Doha, but as I said with Fed and Tsonga not coming and no other top-player available, Doha organizers probably made a big offer to get a top-player.
I don't think fitness is a problem so early in the season after 1 months and a half without tournaments.
But it might be a problem later : might play Davis cup in Canada, then he's entered Buenos-Aires and Acapulco like last year then Indian Wells and Miami and then MonteCarlo-Barcelona-Madrid-Roma ... it might be a problem later than the Australian open, David is not young and he has to take care of injuries as well.
PS : this thread didn't appear on my board at one moment this afternoon, nice to see it's back I'm fed-up with the "X player forum", here I think it's interesting to speak of that packed beginning of the year with a lot of competition to attract top-players.