Originally Posted by rahrens
I believe that you are thinking about the issue of Intel vs. PowerMac.
No, I'm not speaking of Boot Camp.
Tiger was released in late April 2005. At the time, Apple still sold iBooks and Mac minis that did not take full advantage of all of Tiger's features. Most importantly, they did not support GPU-accelerated Core Image effects. They accelerated them through the CPU, but that's not quite the same. (Most prominently, you'll notice through the lack of ripple effect in Dashboard.) But Ireland wasn't even talking about then-current computers, but about computers from three years ago. Three years before late April 2005? In April 2002, the iBooks were still G3s! They don't even even have AltiVec, and therefore don't even support CPU acceleration, so Core Image is almost entirely out of question, and don't bother trying to use both Spotlight and Dashboard unless you use the absolute maximum of RAM.
It won't be any different for Leopard. Assuming it's released in April, you'd have to consider machines from April 2004. Many of those will not fully work with all of Leopard's features. Core Animation? Good luck with that. It'll work, but it will be un-fun to the point that you'll prefer to turn it off entirely. And then, what do you do once applications start requiring it?
This is not to slander Apple in any way, but to put things into perspective. When a new operating system requires modern hardware, there's nothing wrong with that, whether Apple does it, Microsoft does it, or anyone else does it. I've found Windows Vista's system requirements to be moderately reasonable, and the same will probably be true of Mac OS X 10.5 Leopard as well. But that doesn't mean everyone's invited. To develop great software, you have to make compromises, and throwing away compatibility for legacy machines is very frequently one of them.