Chrome doesn't support PPC Macs either..
I can understand that, a 2.5GHz Dual Core is clearly not fast enough to browse the web and check facebook...perfectly understandable why browsers shouldn't support those ancient machines...NOT
The reasons are down to the time vs reward. It's not like they only have to click a button when they compile and suddenly it's compatible with PPC, they'll have taken advantage of technologies that are simply not available for PPC. Yes, they could rewrite large parts of the program to work with PPC, but in some cases the whole point of an update (or even an entire program!) was to take advantage of those new technologies.
Srware Iron (it's like Chrome without the usage tracking) + adblock extenstion = awesome.