I can only think of two OS releases that might qualify for a full version number bump. 2 and 4. And then only because the functionality they brought was significant on a platform level. Developer SDK/API with version 2 and third-party multi-tasking with 4.

Everything else has totally been .1 in significance. But that's kind of besides the point because whether anything changes in the core OS or not, Apple are on a system of revising the major number every year.

And now, unfortunately, the same schedule for the desktop OS. Which IMO is way too aggressive and they should do a 24 month major cycle with 6-10 minor bumps in the middle.

And for both mobile and desktop I'd like to see more of the built-in apps put on their own schedules and updated more completely regardless of OS versioning. Right now it takes a long long time to get anything fixed.