Actually, what's being lost in all of this is that Steve Jobs actually took the time to respond to someone asking a question.
For someone as famous as he, not to mention he's the CEO of an important company and is likely very busy, to at least respond is pretty impressive, and very unusual.
I can't run Windows NT derivatives on my original PC, or even PC/AT! I don't think my Pentium has enough memory either. My i815 based Tualatin can't cut it either, since the chipset doesn't support more than 512 MB of memory.
It's how things are. Apple designed the original iPhone to do what it did at that time. They didn't have the time, and probably wouldn't have had a competitive product if they made it do what they want today (it would have been even more expensive, even if it were possible). So, they probably have the choice of either limiting what their OS could do, or letting go of old hardware support so they could do what they really want. If I were an Apple customer, I'd want the latter.
I'm not an Apple fan (I only have antique Apples), but, I'm impressed Jobs actually responded, however terse, and I don't think Apple is necessarily doing their customers a disservice by choosing progression over compatibility in this case.