While it is true that the current consistency/frequency has little to do with resources used in past development, it has quite a lot to do with what can be committed to current development regarding character creation.
Hell, even Blizzard can't get out from that particular limitation, that they only can only work on so much and adding in other things means taking away development from something (it's why it took them a couple years after first announcing that they were working on new character models to actually get them added, and part of being able to do that, at least according to interviews and such in the past few years, was because it was normally the development that would have gone into a new race or class, neither of which they added in the expansion that introduced new character models).