Assume you're referring to this:
http://www.modbook.com/modbookpro
Yeah, a solution that relies on buying a new MacBook Pro, throwing away the case and expensively hand-rebuilding it as a tablet is a good basis for comparison here.
Alternatively, look at the number of iPad stylus products on sale (e.g.
http://www.adobe.com/uk/products/ink-and-slide.html - and
many more) - maybe there's a demand? The current stylii range from 'plastic fingers' (which aren't much good) to more sophisticated active ones with bluetooth (which are hampered by the lack of a standard stylus API). Then, for OS X, there Wacom Cintiq tablets are pretty popular considering the pricetag (and that they need a Mac to work).
Yes, he was talking about an iPhone with a 3.5" screen with a very limited CPU vs. Windows Mobile phones with even smaller, grotty resistive touchscreens that needed stylii because the buttons on the on-screen keyboard were too small to press with a finger (I had one of those - they blew).
Things have changed beyond recognition since then - we're talking about devices with 12" super-high-res screens and multicore CPUs that are quite capable of running powerful graphics apps.
NB: I don't think its likely that the iPad Pro would run OS X, I just think that it
could be done with a force-touch screen.