Well, "good" is a little subjective. I am purely speculating here, but I doubt that Apple compiled something into the code to make it simply not run on first gen hardware. IE: there must be something about that hardware platform that makes it different enough from current-gen hardware that supporting it adds some amount of back-end effort. Perhaps the reason has to do with one of the other factors I mentioned, a "mistake" or shortcoming in the first-gen hardware that requires more internal hacks and work-arounds in the code than they are willing to support.
It's not like this sort of thing is unique to Apple. Some of the first-gen Droid phones are not going to see the 2.2 update. Yes, there may be more hardware variants and changes among the Droid phones, but it is still a relatively new platform abandoning not-that-old hardware.
It would not be the first time - the first iMacs are capable of running up to MacOS X 10.4, provided they have enough memory. I have successfully ran 10.4 on a beige G3. The installer, however, checks the hardware against a list of "forbidden" (if I remember the term used in the .plist file) machine types.
Here is a similar story, regarding 10.5:
http://www.macosxhints.com/article.php?story=200710260837463...
The reason I asked is because, as far as I know, the processor and the amount of memory is the same for 1st generation and 2nd generation hardware. I wonder if Apple is artificially limiting the availability of their software just to force fashion victims to buy new hardware.
And calling the hardware base iOS has to support "massive" is quite an overstatement. That's the enormity of 7 models.