Leaving them at 30 lets level 10 archer towers (th8) take out a skeleton in 1 hit (32.5 per hit), which is too big of a nerf imo.

Increasing their HP to 37 makes level 10 archer towers require 2 hits to take a skeleton out, while letting level 11+ archers only require 1 hit (37.5 per hit for level 11)