OS X is primetime. Some Apps fell back to the midday soap opera status, and some slipped way back the the previous nights infomercials. The OS itself is finished, and has been for a while.
No reason why somebody would hold themselves back. If your "killer app" hasn't been ported, it tells you what they think of you as a customer. It's been a long time since OS X was introduced, and companies that aren't here yet are just plain ignorant of the user's needs.
Nothing about the OS is holding users back (trust me, there are plenty of people still using 8.6 out there that don't realize they are able to upgrade the OS on their computers) At my old job I would get plenty of people calling in "I have an iMac 9.0", Me: "what kind of imac mam?", "An iMac 9.0, I told you allready". riiiiight... those people should never upgrade, ever. They should use the machines until they die, buy a new machine and the "for Dummies" book on it. Little bug fix and firmware updates should be done, but a point release, no way. It is easier for both them, and tech support.
But if you are a professional and you are still using a classic operating system, you need to get with the program, before your left in the dust. And consumers and good 'ole mac addicts, just do it, nothing stopping you other than the money and install time.
I know this may be offesive to some, and I really don't mean it that way.