I am guessing that iOS is the long term future OS for Apple, not MacOS. As iOS continues to evolve and get more features, more and more people will be able to use it as their only computer and Macs will become increasingly niche products used for specialty cases.
"When we were an agrarian nation, all cars were trucks, because that's what you needed on the farm. But as vehicles started to be used in the urban centers, cars got more popular … PCs are going to be like trucks. They're still going to be around, they're still going to have a lot of value, but they're going to be used by one out of X people."
-Steve Jobs, 2010