A lot of mmos do this. The only thing WoW pioneered, in this aspect, is retaining the look of old gear via transmog. No other mmo allows the use of old gear once an expansion is released, that I am aware of. Final Fantasy has a slight spin on what Wow did. I've played Rift, Wow, SWOTR, ESO, EQ, Tera, Wildstar, FFXIV, and a few others. None of them really let you use older gear for the new stuffs. Essentially, we grow as the game grows. Can't really convince people to use new things if they hoard the old stuff.