Actually, iOS is not OS X, nor any other flavor of Unix. Although Apple is happily attempting to scale up iOS to tablets (and presumably other devices), I doubt it will have either the flexibility or the longevity of OS X; as more powerful processors become more widespread in small devices, limited operating systems like iOS will lose out as users clamor for true multitasking and full-blown application software (rather than lots and lots of miniscule apps).

Edit: after investigating a bit, I find that I am mistaken -- underneath all the UI cruft, iOS appears to be running some version of the Mach kernel. That makes it a lot closer to the Android model than I thought. It also means that, if Apple should ever find the interest in doing so, they could scale up iOS fairly easily...