I laughed out loud when I saw that line - good to see Apple focusing on the important parts!
I think the difference is speed - on my iMac DV/400, having Quartz rendering on was painful before this. Now it's usable, and I left on through my entire endgame last night without being annoyed with it. It's a bit like comparing OS 9 to 10.0 to 10.2. 9 - no Quartz rendering - is still fastest, but 10.2, ie Quartz with the 10.2.4 update, is fast enough for me, while 10.0 was borderline.