The caster +1 dmg feats are even worse in that they have stat requirements - for stats that you're likely to not have much use for - and don't scale. Whereas anyone can take weapon focus and its damage increases by tier.
While I've been thinking similar things as your post, the caster feats <i>do</i> scale with tier, at the same rate as weapon focus. There's just no similar feats for all the other melee feats in the PHB. Hopefully, it'll change with PHB2, but that seems to be the earliest it can happen(baring Dragon articles).