This is probably an easy question for hardcore GNU/linux folk. I know the basics of Linux, and have used it lightly for the good part of a decade. I am curious why the repositories are usually a version (or two or three) behind the latest stable release of many given software packages. For example, I have read about the new single window mode in Gimp 2.8, which apparently is also stable. My update manager indicates that mine is up to date, but is only 2.610-1. I've noticed this with firefox in the past many times as well, and can only assume this is the case with lots of other packages.
I don't find this to be any big deal. I'm not some die-hard, bleeding edge type. I just find it kinda odd and am curious as to why.