I don't see it as a necessity. I played XI for years voice chatting using combinations of Vent, Skype, TS, and XBL chat based on who had what available. Yeah, it's overly complicated but, in my opinion, a good enough solution that SE doesn't need to spend their already-strained resources on it.
(Although, believe me: trying to use XBL chat with a wireless controller, included headset, and a silver account while playing on PC is a pain in the ass)
Also, Teamspeak has an official Android app as well.
