I think I agree with jms, an easy analogy would be that if you were a Mac user, you used Mac OS X 10.0, then 10.1, 10.2, and then 10.3 with your Power Mac G4, but when you upgraded to a G5 you had to go back to 10.0, 10.3 was not compatible.
Having now used an Iyonix, I can see what the Select fans are talking about, whereas before, I quote frankly did not see what the fuss was about. Select has some stuff (like alpha-blended PNGs) which allow you to achieve effects which are just not possible on an Iyonix. Not until (if) Vantage appears on it, anyway. That's not to slight the Iyonix in any way, it's cool, it would just be cooler with Select.