I'd assume it is using hardware since it requires the latest MiniGL. 28fps should be playable enough for most people. As Thomas says, it needs optimisation.
For comparison, I've gathered the following results (some my own tests, others from the web)
Apple iBook G3-500 / ATI Rage 128 = 10 fps
Pegasos II G4 1Ghz / Radeon 9000 Pro = 40 fps (from OSNews)
Apple PowerMac G4 1Ghz / Radeon 9000 Pro = 95 fps (from Barefeats)
Intel P4 2.4Ghz / Radeon 9000 Pro = 191 fps (from Sharky Extreme)
Macbook Pro 2Ghz / Radeon X1600 (stock settings under OS X) = 296 fps
Macbook Pro 2Ghz / Radeon X1600 (clocked up under Windows XP) = 384 fps
Athlon 64 X2 4800+ / Geforce 7800 GTX = 500 fps
Apple PowerMac G5 Quad Core 2.5Ghz / Geforce 7800 GT = 600 fps (from MacRumors)
Looks like what's needed is a Quad-Core G5 Amiga :-)
I think the difference in results between the PowerMac G4, the Peg G4 and AmigaOne with the same GFX card can be down to the lack of hardware T&L support in the AmigaOS and MorphOS Radeon drivers.
