Certainly there's an element of gamesmanship in all of this. In fact, Pete being Pete, it wouldn't stun me if he's telling Harvin to tweet such messages of inspiration. War, business, marriage...always best to keep your adversary unknowing and off balance.
As alluded to 1,000,000 +/- times, it wouldn't be wise to bring Harvin back any sooner than absolutely necessary. That shouldn't be the case over the next 3 weeks. Some fear that not getting him actual game time will hinder his production when called upon. Every report I've heard from our players and staff alike, suggest our practices are very competitive and rival actual games in intensity. I am confident the likes of Sherman and Thomas can duplicate anything the Saints or 9ers can throw at Harvin. Better to keep him in a more controlled environment at this time, IMO.