Because I think the conditions and main concern of this squad changed. I think they realized with Daniels injured, Pierce would have to guard LeBron or Carmelo for the bulk of a seven game series. Obviously, that's something they don't want, especially at how it would take away from his offensive game. In 08, the Celts used Posey and in 2010, the Celts used Tony Allen to put on LeBron. The 2011 Celtics until yesterday didn't have that (NOT SAYING JEFF GREEN IS A LOCKOUT DEFENDER OR WILL BE SOMEONE WHO SHUTS DOWN MELO OR LEBRON, GREEN JUST PROVIDES ANOTHER BODY TO THROW AT THEM, BIGGER AND MORE ATHLETIC ONE AT THAT).
Also, the Celtics I think realized the competition for the ring is not only LA or Orlando but its also Dallas, S.A., Miami, NY (I don't care what anyone says, as much as playoff slows down, Melo and Amare can single handling win a series or two) or Chicago. With that said, I think realized they may need more flexibility. With Jeff Green, the Celtics now can throw out a lineup close to the one they ended games with in 08.
08: PG-House or Rondo, SG-Ray, SF-Pierce, PF-Posey, C-Garnett
11: PG-Rondo, SG-Ray, SF-Pierce, PF-Green or Big Baby (Dependent on if they need someone to spread the floor or some muscle inside), C-Garnett.