Yeah, which is actually a little annoying. I thought part of the whole point of Mega Evolution was to give Pokémon that had been largely ignored by the fan base a competitive edge. I mean...Mewtwo, Charizard, Metagross, Gyarados, Tyranitar, plus the two you mentioned...
These are not Pokémon that people have any problem remembering. I get Charizard, cuz, you know, its a starter and I think all starters should get at least one mega, but the others I have a hard time reconciling with the principle. If the purpose for giving Slowbro and Altaria and Mawile mega evolutions is to out them on the "same level" as these others, well doesn't giving those others Megas sort of defeat the purpose. That's why I hope that Megas from now on are given only to middling and/or weaker Pokémon. No more pseudo legendaries. Legendaries, maybe, cuz their whole purpose is to be the most powerful Pokémon around.