Vince:
You're correct about most of the recoil in a "springer" being in the forward direction. It is also true that many scopes on the market are still made with internal bracing to cope with forward recoil only.
So where does the recoil pad come in to play as a "scope saver"?
Well, it isn't just the forward recoil that kills the scope. It is also the rapid, "double-snap" and change in direction that helps the death process along.
Just as the recoil pad "spreads out" this recoil on your shoulder, it can also contribute to spreading out the "time moment," for lack of a better term, in the transition from rearward to forward recoil. In other words, it can take some of the "snap" out of the spring-piston rifle's unique, bi-directional recoil.
-JP