the manga doesnt usually include useless stuff.....

keep in mind, that the manga version of haku and zaku's flashbacks are MUCH shorter than the anime versions....
for them to pull out all new flashbacks at such a crucial time.....you'd think that he's trying to clue the readers in on something new that is good to know with regards to this whole sasuke being evil ordeal. The flashbacks showed a side of itachi that none of us knew, so dont be saying that its nothing new for you, Sidnne.

And you guys shouldnt jump to any hasty opinions about it until the flashbacks are done with. Far too many times do i see people quick to bitch about something, only to find that next week more than proves the logic behind the occurence of the offender in question.