The price and ease with which Apple owners can upgrade to the new operating system might help explain why Mountain Lion saw what Apple says were a 3 million record downloads in four days. Though the latest from Apple offers over 200 new features, overall the new OS is a lot of the same, as the reviewers explained. So how, then, did it do better than previous models? Some plausible theories: 

• Even with the meh reviews, most of the reviewers said at $19.99 the upgrade was worth it. The previous release, OS X Lion, was priced at $29.99 and Apple reported 1 million downloads in the first 24 hours it was available on its App Store. Generally a cheaper price equals more sales.
• There are more Macs than ever on which to put the new OS. Apple's latest earnings report cited 4 million Mac sales just last quarter, a 2 percent increase from one year ago. As of January 2012, Apple made up about 15 percent of the computer market, up from 12 percent the quarter before. More Macbooks equal more upgrades. Though, note to older Macbook users, the upgrade isn't compatible with certain makes, such as the 2008 black Macbook.

With those factors, Apple gets to say it has put out its most successful OS ever -- even if it is nothing special. 

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