iOS: 2007-2011 four updates at one year intervals before the decline in quality that lots of people perceive starting with iOS6. Again, hard to say one year is the culprit.
I do think Apple needs to restrain itself, and work on figuring out which features can be shipped without compromising quality. But whether it needs to do longer releases or do smaller releases is hard to say.
As for Mac OS, when I read Siracusa's review, I was thrilled. There aren't consumer features, but they're doing so many things to make desktop machines more responsive and efficient. It's even more exciting than Snow Leopard.