I doubt it. Honestly, stop promoting that POS tablet already, I'm not buying it, a lot of other people aren't buying it (or will, but still use their desktop as a main platform.), so shut up and start giving us some actual hardware news. We came for info on computers, not tablets.
Also they said mobile, they didn't say tablet and smart phones. This would include laptops. They also didn't say they were only accessing it via cell phone providers, these numbers still reflect people using said devices on their own home networks. I know that some of my friends have stopped using their desktop in favor of a laptop that can move around the house. It seems logical that with a wider device base this prediction is not all that far fetched.
The problem I keep seeing is a strict definition of what a PC is, I've seen some studies say that laptops are PCs while other say no, laptops are mobile devices. Some say PC's are only PC's if they use Windows, which is silly. So until there is one definition that every study uses, which there probably never will be, they need to specify exactly what their specifications are for a given category, otherwise they do themselves and everyone who reads their study a disservice.
I'm not so sure about the US. But here in the UK we have more mobile phones than we do people. So surely its natural that as time progresses the number of people accessing the internet through their mobile will tend towards 100% as they upgrade their phones and business' want their employee's to be more connected when out of the office.
The idea of traditional PC internet users stagnating and declining is also taking a very biased look on things. In both the UK and the US the ammount of the population that is using the internet was above 80% in both countries. Its obvious that it will stagnate now. Whats more obvious is that people will be using both traditional PC's and mobile devices to access the internet.