Only in Apple marketing terms. And that way you'd have to include OS X Server as the third flavour.
But in terms of the system, iPhone OS is related to OS X only as much as Ubuntu is related to the embedded Linux running on a router.
Something that I've heard is that Mac OS X client has all the functionality of Server, but Server just has pretty GUI apps to control the server functions. I could be totally wrong, so don't quote me on that.
Something I would like is a single combined software install, removal, update, & app store app
with the ability to use other apps (bold so people read it & not just what comes before). Here are the basic functions explained:
-Install: same thing as Installer.app
-Removal: looks up all the apps you have, see where all their files are, etc. & deletes everything. Give an option to delete one app in a suite & not delete a file that's shared by multiple apps
-Update: updates Apple software as well as 3rd party software. Lets you not have to hunt around to see if there's an update for your app.
-App store: a central location to buy Apple & 3rd party apps. Include an option to buy software for someone else. Also, have an option to show all apps, only apps where you meet the minimum requirements & only show apps where you meet the recommended requirements. And make it easily searchable & have different categories (ie Lifestyle, Health, Education, Games, etc.).
Though I want to be able to get my software from somewhere else, too.