"Mash" moves aren't too bad. I play Chun and I play on fight pad. Mashing is one way to do it, but not the optimal way. Try something like lk, lk, then mk. The mk will do lightning kick. The lk's buffer the kicks. No mashing required.
Now try to do that with a Dualshock or any other non-fightpad. In SFIV you need 5 presses in a very short period of time to activate. While it is possible to do it in a way of mashing and pianoing, it's still extremely bothersome. There is a good reason why SFxT didn't have it either.
These characters(Chun, Gen, Blanka and Honda) are also the only ones I can not use due to those specific moves, their execution and the importance of those moves in their respective gameplan.