Generally Gamefreak stays pretty consistent with the previous game in that way. The result of their refusal to just say "Ok, Magmar evolves at level 45 or whatever now" is that too many game mechanics are introduced, IMO. The method of evolution of a new Pokemon in an earlier line always is one that just wasn't available in the previous game. The suggestion being "They could always evolve, it was just you who couldn't do it."
See the Magmarizer/Electirizer, the holding of incenses for new pre-evos, new evolutionary stones, the evolution upon learning a specific move, which IS added at a specific level and so on. Anything to avoid just inserting a levelled evolution where previously there was none.
I appreciate the consistency actually, but it could be tightened up.
