I've heard this dreck for well over a decade now. Right up there with "year of desktop Linux" which really has never happened. Linux was never a threat to Microsoft and windows on the desktop. Linux killed the Unix venders.
Linux is not a threat to apple. Hell apple now maintains some key components that Linux widely uses (ever check and sees who owns and maintains CUPS these days).
And Linux is not dominating the mobile market. While android may use Linux underneath, when people by a droid phone, they think google and android os.
What keeps people like me using macs and windows are two factors. Ironically the same two factors to why I switched to osx over 10 years ago.
1) Lack of major software packages. For better or worse the business world runs on office. Personally at home I can get away with using OpenOffice or iWork. But for work, I've tried and always end up having to use office for some reason.
2) lack of quality hardware - on the server side Linux has this, not so much on the desktop and laptop side. Even windows now have this problem. I buy MacBook pros because I have yet to have one that has lasted under 4 years. Think pads used to have this level of quality, which you also paid for, but over the past 18 months I know a lot of people we work with are complaining that they are on their second or third think pad in that time.
Maybe as we get more cloud based apps this will change. I'm finding office 360 and skydive increasingly handy as I can now edit office docs online with either an iPad or android tablet easily. But seriously, Linux is still not a threat to either company.