If you actually stand back and think about it, some of the most popular apps on an iOS device are centered around text input for storage of information or for use in some kind of communication like an email or text message. Native apps like Messages, Mail and Notes are all heavily based around text input and would just be useless shells without it. Apple obviously offers an on-screen keyboard that is easy to use and intuitive, but just because it is the standard method of text input it doesn't mean it's the best.
