Here's all the information you need to know: in just 5 years of iOS (under 2 with the PC successor, the iPad), iOS devices now make up 72% of Apple's earnings as of last quarter.
... and the graph is on a sharp uphill climb. In another year, it's predicted that that number will breach 80%. When 8 out of 10 of your customers are buying an iOS device, when does it make sense to continue supporting the remaining 2 customers? In another 5 years, it'll be under half of 1 customer per 10.
Think of which jobs today can replace a notebook or desktop with an iPad or iPhone: Retail, Mobile sales agents (real estate, pharmaceutical, etc), educators, medical professionals, are just a few I can think of right away. Add in all the jobs that don't require a computer at all, and this represents a significant portion of all jobs. All that remain are niche professionals such as engineers, writers and multimedia content creators.
Writers can easily solve their issue with the addition of a full keyboard. Engineers, Video, photo and audio professionals are those who still need a Mac/PC but some of those are already being addressed.
All you've got left are the manufacturing industry. You won't see iPads running a production line but then again, it's unlikely that you'll have seen a Mac doing that job anyway. These are highly specialized fields that will have customized computers doing the job.
So where does that leave the Mac in the next 10 years?