Consider first of all the scope that expertise gives to a player who wants a less than optimal race/class combo. Such a charcter will likely start with a primary stat of 16 and an expertise feat gives him a convenient leg up.
And if this had been how the feats were designed, it might have been much more tolerable. For example, if expertise for a ranger had required int 14 or something (aka something the ranger doesn't normally get) then the feat becomes a lot more balanced. It will only be given to characters who don't have optimal stats, and so is a feat mainly designed to balance out "weak" builds, not further increase the power of strong builds.
As it currently stands though, strong and weak builds both can take the feat, so its not doing the weak builds any favors.