> maybe there hasn't been the demand as the 1.8Ghz Sonnet is duel cpu.

By that logic there wouldn't have been demand for single 7448 at 2.0 GHz for older PowerMacs G4 neither. There are dual 7447A/B at 1.8 GHz as well as dual 7448 at 1.7 GHz for the older systems.

http://www.lowendmac.com/ppc/g4upgrades.html