When they need to revamp the architecture entirely. Apple really took a gamble with OS X. They were quagmired with the System 9 line - they could have kept inc

When they need to revamp the architecture entirely. Apple really took a gamble with OS X. They were quagmired with the System 9 line - they could have kept incrementing, but it was obvious they'd hit some limits. I think one thing people forget is how bad OS X was when it first came out. It was slow, missing key features, and was just plain buggy. It wasn't really until Tiger that they had something ready for the mainstream (imho). But they took some risks - especially with the rendering approach w/ Aqua - and as hardware caught up it started to pay off. The features they can slip in today are really the result of some brave design decisions a decade ago (the Intel transition is another example). It was somewhat easier then because Apple's market was still a very hardcore group. Now, it might be harder for them to go through such a revolution - the market might just rebel against them... The downside to brand I guess. Of course, Apple made a good move with the iPhone - this is a totally different evolutionary path that might be a better bet (i.e. Perhaps there won't be an OS 11, or if there is by the time it comes it might not be as big a deal as other things).