Apple's market share is 66% for all personal computers sold in stores for more than $1,000. In addition, Apple's market share as been increasing as sales of PCs as a whole have been dropping.
Are you serious? Those are sales figures (sold new at retail stores in first quarter 2008 for over $1000), not usage figures. You're not talking about what's being used in the market, just what was sold during the first quarter - OF 2008! - and even then you're only considering retail stores and $1000+ computers, where the average PC cost is $650. So not only are your sales figures irrelevant to a discussion about usage share, but they're cherrypicked to such a ridiculous level that they're not even relevant as overall sales figures. That's like saying a large percentage of the cars on the road are Cadillacs because, in June of 2010, they sold the most domestic cars that cost more than $40k. Most cars cost less than that new, many cars aren't bought from domestic dealerships, and most of the cars on the road aren't new or weren't bought new in that time period. Likewise, most computers don't cost that much, many of them aren't bought from retail stores, and there are more computers out there than what was bought new in the first quarter of 2008.
The GP's point was that Mac's desktop OS market share is less than 10%. And that's not only true, but it's generous - as of 5/2012, they've got about 6.5%. Like it was mentioned earlier, less than Vista.