>> "My theory is that a lot of the really experienced engineers (the one who started with NEXT and OpenStep) left when they were rich after the iPhone stock jump."
While possible true I think the real issue is resources being spread too thin. Remember they had to delay the release os OS X one year as all their engineers were working on iOS? Now they're doing yearly releases of both OS's. I'm sure they've hired more engineers but pre-iOS there were probably lots of engineers who had been working exclusively on OS X for years and were able to maintain quality. New people take time to get up to speed.
While possible true I think the real issue is resources being spread too thin. Remember they had to delay the release os OS X one year as all their engineers were working on iOS? Now they're doing yearly releases of both OS's. I'm sure they've hired more engineers but pre-iOS there were probably lots of engineers who had been working exclusively on OS X for years and were able to maintain quality. New people take time to get up to speed.