This isn’t even entirely true. They started pushing their releases back so much that it became two years, but it was originally supposed to be yearly. And it was for the first several versions.Well, they released it on a 2-year deadline.
10.0 Chita: march 24, 2001
10.1 Puma: September 25, 2001
10.2 Jaguar: August 24, 2002
10.3 Panther: October 24, 2003
This is where the time between updates started to lengthen
10.4 Tiger: April 29, 2005
10.5 Leopard: originally announced for fall 2006, delayed to spring 2007, delayed to October 2007 due to iPhone development.
Released: October 26, 2007
10.6 Snow Leopard: August 28, 2009
10.7 Lion: July 20, 2011
and this is where the yearly updates started back again.
And it should be noted that the initial 10.X.0 launches of tiger, leopard and snow leopard were riddled with issues, so it’s not like the longer wait time gave that much of a benefit when it came to bugs.
As pointed out earlier up thread, snow leopard launched with some nasty bugs that completely erased peoples data.
Also, best not to mention Windows Vista, software that was delayed so many times it became a joke, and when it finally launched (five years and three months after the previous version) it was a mess.