Applications for a laptop, medium touch tablet , TV set GUI and a phone are not just needing different GUIs but also need different design. On a decent screen multiple windows and floating & dockable customisable tool bars might make sense. But never on a phone, rarely on a tablet. TV is similar display needs to a 6" tablet, (because it's maybe 2m away) but due to very limited user input and navigation and usually no touch, no keys much beyond 0 .. 9 and functions and no trackball/mouse (why not a IBM thinkpad style or gamepad wobble pad/stick though?) is mostly limited to browse & select.
One App store, one name of OS and one GUI is just a confusion. At least Apple and Google differentiate a bit (iOS, OS X and Android, Chrome).
After trying to shoehorn the Win3.x then Win95 style on everything they make the opposite mistake of Zune interface on everything.
By all means have a single coherent API for all devices so programmers have less to learn and make less mistakes. But this doesn't mean you should normally do the same application identically for all platforms. Unless it's maybe a game with simple interface or a trivial program. Even then it might not want to be full screen on everything.
Even running phone apps on a PC in a "phone/small tablet sized window" is rarely going to work well. Touch vs keyboard and mouse with no touch.
Most phone apps are either too trivial, or awkward or more limited than many paid or free programs on a Laptop. Also I want to get away from MS dependency on desktop, not get locked into it.
I can use the phone on WiFi beside laptop anyway.