Something very odd is happening at Apple. Either there is a massive shortage of developers (unlikely) or developers have been moved to a new project (AppleTV ?). Because Mountain Lion and iOS6 are by far the most underwhelming updates yet in terms of features.
It actually makes for a nicer development model than the 'everything doesn't work for a year and then miraculously comes together 4 months before release' development model. For example, with Snow Leopard, XCode became garbage collected and was unusable for like 50 releases in a row.
Ultimately, while you get a slightly less buggy release that comes out on time more or less, the features seem less ambitious.