madamimadamtimallen posted this Newsfactor article from the 27th which explores why Mac processor upgrades have not progressed:
Aside from the technical issues, Sonnet said current pricing on the latest G3 and G4 chips makes faster upgrades impractical.
"These new chip prices are high, so the economics do not yet work out to offer the market a reasonably priced product," Hsu told NewsFactor. "As the new G3 and G4 chips become more available and prices start to fall, the economics will be better, and processor upgrade manufacturers will be able to offer products at affordable prices that make sense to the consumers."