Most people still don't care about having email on their phone: that's not what they use their phone for most of the time. They use it for text chats, taking photos, playing games, navigating, etc. I'd say email ranks pretty low in importance.

Those other companies failed because they had clunky UIs and thought that most people really cared about typing emails on their phones; they didn't. Apple finally proved that people want something easy to use that does things they want to do (which isn't email).