I use an Android; it has copy-and-paste. I believe I have used it exactly once in over a year of using the phone - I had started composing an SMS to the wrong person and decided to copy/paste the text instead of simply typing it again.

For most users, I am guessing the most common use case is copying a browser link to an email/IM/SMS, and this can be supported without an actual copy/paste implementation. The hard part of full-blown copy/paste isn't implementing copy/paste storage, it is figuring out the UI for selecting text on a touch screen.