The first versions of Mac OS X only supported software rendering. GPU compositing didn't show up until 2003, in Mac OS X 10.2. It was branded as "Quartz Extreme".
I did not know that! There was about a 6-7 year gap between 1997-2004 where I didn't really do much with Mac's. But your timeline seems spot on, it was 10.3 when they introduced Expose into the system. A great demonstration of the GPU functionality in action.