For every new wave of computing - mainframe, minicomputers, PC, client-server, web 1.0, web 2.0, cloud - there has been this talk about the immediate disappearance of the previous wave(s). It just never happened. Mainframes and Cobol are still - some 50-60 years after they first appeared on the market - in demand.
Linux on the desktop/laptop appeals to people experienced in computing using laptops or desktops. That's a nice & that's good - it's a defined target group and they know what they want! It's large enough for now; millions of users and it's growing with a growing total market. With a keyboard and large screen you want a functioning desktop - not something targeting phone or tablet users. You want a stable, secure OS, applications, efficient use & supportive community. Sounds like Linux to me.
MS is in terminal decline. They will disinvest in the desktop, not enough money there; they are targeting servers applications and will be forced to open up in order to support "bring your own device".
It's a mistake to exclusively target the Linux desktop for phones and pads. Wrong kind of users. Go for the laptops and desktops. Lots of old hardware out there with XP on it that won't run Win7/Win8 either because of hardware or license costs. And there are plenty of disgruntled MS users around. Preinstalled and easy install is key.