I'm not convinced that PC sales have actually stalled.
Also, that there is a substantial conflict between "handheld devices" and "computers" (laptops, desktops, et cetera), seems like a false assumption to me. Sure, some handheld devices offer some of the same functionality, but so what?
Are some people getting handheld devices instead of more traditional computers? Probably. Are handheld devices replacing computers? To some extent, perhaps, but overall so far, not really from what I've seen. Just because more people are buying handheld devices doesn't mean people aren't buying and building computers. I'm thinking that it is the rate of growth of more traditional computer sales in comparison to mobile devices that may have "slowed down" rather than the number of those kinds of computers being used and bought.
Personally speaking (so perhaps not all that relevant), I've bought more traditional computers and computer parts more recently than I ever have before. I've also bought newer handheld devices, but less frequently than traditional computer parts. I know I've spent a whole lot more on traditional computer parts overall, recently, and even on individual components recently than on handheld devices. But yes, I'm not most people.
I'd like to see a comparison of when and how many people have had "traditional computers" in their households and at their places of employment. I'm guessing that the general trend for this number has only gone up, even taking into account population growth.
Likewise, I have more "traditional computers" and computer parts in my household and place of employment than I ever have. As far as I know, that's also the case for everyone that I personally know, including my parents and their household.
So yeah, I find the notion of there being a significant conflict between traditional computers and mobile devices to be false. A purchased mobile device does not mean an unpurchased traditional computer. Likewise, just because there are more mobile devices being sold than there have been previously, it doesn't mean traditional computers are losing out on that market, since they're different markets, though they may have some overlap. It's kind of like trying to compare the sale of houses/apartments with the sale of automobiles in the previous century even though some people have mobile homes.