I think his point is not so much OS X vs. iPhone OS, but rather OS X applications vs. iPhone OS apps. The underlying OS matters, sure (see Windows vs. OS X), but the key thing is the applications (and screen size).
Given his business needs, certainly he'd want "real" accounting applications, word processing, spreadsheets, etc. not to mention the ability to connect a keyboard, mouse and screen. That makes one think of OS X instead of the iPhone OS, but it's really the apps and if/when those types of apps are available for the iPhone OS, then the concern over what OS the tablet would run would disappear.
You cannot run desktop apps written for x86/ppc on an arm chip. It is impossible without rewriting and recompiling the apps. Any tablet running ARM will be running iPhone apps if anything (probably with minor modifications required), it will never run desktop apps. So if you consider non-desktop apps to be not real enough for you, please buy a laptop which runs OS X, has a keyboard, trackpad, and screen which make those apps usable, and stop complaining about wanting 'real' OS X.
Personally I don't think there's any point having a tablet which turns into some kind of desktop surrogate, because it would have to compromise on the stuff that could make a tablet great. That's already been tried and found useless with Windows combo tablet/laptops - they're more laptop than tablet.