These numbers really don't convey the important questions, of which there are arguably two.
First, what is the OS split for newly installed systems? It was once simple to know that if Apple sold a Mac it ran MacOS. No longer. They make very nice laptops that can run a competitor's OS. Similarly a PC, although it can't run MacOS, can run many Unix variants. How much of the increase in Mac laptop sales might be attributed, not to users fleeing Vista, but to users installing Vista?
Secondly, what are the manufacture's shares of the market? It isn't the brand-names. They don't make anything anymore. The real market split is between Acer, Asus, Mitac, Wintec, Quanta, and a legion of other Taiwanese companies. Companies that might sell a few things under their own brand-name, but for the most part the lions share of their business is as the faceless powerhouses that create the computers branded by the so called market share leaders.
(To avoid too many flames, this was written on a G4 17" Powerbook.)