Well, I can assure you that they're mistaken in assuming that the cursor drop-shadow is a Quartz Extreme indicator. My mouse pointer has the shadow on both the monitor connected to a PCI Radeon 7000 (32MB) card AND the monitor connected to the stock PCI Rage 128 (16MB) card.
I have not found one definitive answer to the cursor drop-shadow phenomenon. I do not think... in fact I am almost positive... that it indicated Quartz Extreme, simply because Quartz Extreme is NOT enabled on my system, and I verified this with the "QuartzExtremeChecker" software available on versiontracker.com.
Perhaps it is an indication that you have a graphics card with 32MB of RAM, therefore, you have the "recommended" setup for Quartz Extreme, regardless of whether your card is PCI or AGP or whether or not Quartz Extreme is actually enabled.