that's only cause Rossi know how to win!
a good "winner" always try to win at the slowest pace possible!
and that's what he does!
He follow the leader until the 4-5 last lap until he decide to pass him! after he incresed the pace a bit to be sure not to be pushed to hard!
It have a lot of advantages!
If the leader cannot make a more than 1-2sec lead on the follower the spectacle is way better for the viewer, which leads to appreciation and wanting to view the other races!
Rossi is the undisputed King of MotoGP, but all other rider do excellent race and give a good show with really nice passing(sometimes pretty hardcore

)
Melandri have a great talent too(when he doesn't fall at every race

like last year)