Did you not notice that Apple completely controls the ecosystem? Give M$ credit. They have to support thousands of hardware products with their OS. Considering that fact makes Apple look silly in comparison. And don't get me started on supporting them on a Windows network with real security. They make consumer products not designed for enterprise use.
Why do you think the Apple sales reps avoid IT like the plague and try to sell directly to end users?
You are saying that Apple controls all those third party routers it connects too? We're talking about WIFI aren't we? Do they also control printers, blue tooth devices too? Notice that these are the devices that have issues right now.
These days, especially with IOS releases, tens of millions of new devices are suddenly put in contact with tens of thousands of different WIFI routers and blue tooth devices within a few months. There is nothing comparable in the PC world. Mobile devices also tend to be in contact with many different types of routers/printers (compared to only a few for PC's) with environmental conditions that vary immensely.
If you buy only Apple devices, then I'm sure the number of issues is on average less than with third party devices. But, even those could have code paths that haven't been exercised until now in their OS.
Sometimes problems occur simply because the default way the protocol is implemented in the new version of the software reveals bugs that already existed in the third party device and had not showed up in normal use yet.
A different way of reacting to traffic on the WIFI segment could impact throughput or connection stability. Someone with less local traffic or a different router could not be impacted at all by such an issue.
Or, sometimes more subtle could occur, like changes: to the way DNS leases work, to how security works (problems connecting with the router), etc.
Systems integration issues are hard and Apple with its every growing user base and very quick release cycles has its work cut out for it.