Like I said, I'm cool with that. If you take the WC3 models for they priestess and mage (I'm not sure what the exact name is, bother are basic human spellcasters) they both look similar (high elves). Those 2 being given as 2 skins for the same hero is okay. That is what it sounds like LoL is doing, which is okay. Now if they added another skin which looked like an orc raider or something, which is a different race, different size, and it's attack animation is radically different (throws stones as opposed to casting little energy balls), there's room for confusion. It does NOT sound like LoL is doing that. So again, LoL is okay.
BUUUUT, the ability to permanently unlock heroes who might be unavailable to other players is a no-no. Tolerable in a free game, but not in a game I'm expected to play for. If I have to pay $15+, any advantage, even as small as that, should not be possible via micro-transactions.