Responding to the recent, above posts, for LT2 to be adversely impacted by the presence of a new QB, that new QB would have to completely fall on his face.
I've seen enough evidence in recent seasons of a first year QB with more than one year in the same system come in and perform at a high level (See Tom Brady, Carson Palmer, Marc Bulger...hey, even Drew Brees). These guys weren't perfect, don't get me wrong, but they posed more than enough of a threat in the passing game to keep defenses honest.
Rivers is in a similar situation. Unlike Eli or Leftwich or Alex Smith (Berger is the exception), he is not coming into a hostile situation in just his rookie year and expected to run an offense. Heck, in Rivers case he has two full seasons in the Charger system along with the same coach, same personnel (save for Reche Caldwell

)
As for LJ, I don't believe the loss of Roaf alone would dramatically impact his performance, as the eveidence from last year showed KC was still productive running the ball. However, when you add in the loss of Vermeil, Saunders and Richarson, as Loomba just mentioned, it can't all bode well.
For my money, I'm sticking with LT2 as the #1 pick for all the reasons stated above.