First of all; the end cycle of Win7 officially sits at 2018.
Also; I don't see the end for PC's coming anytime soon. There are tasks which are more easily done on a PC just like there are plenty of tasks which can be easily handled on a phone or tablet. Just like some other poster mentioned how laptops are commodity; the same basically applies to PC's.
For most people a PC is a tool you turn on and can then use to perform tasks. Nothing more, nothing else.
For most of those people in my surroundings the most compelling reason not to look into Windows 8 is either because their current computer works just the way they want or because they followed my advice to look into an upgrade now before you can no longer get Windows 7.
The fun part; the most compelling argument for that upgrade (according to some feedback I got) was that I could make Windows 7 relatively well behave like XP, but that this would hardly be possible with Windows 8 (yes, I know there are plenty of tools which can mimic the start menu behaviour, but even so..).
In short; most people I met feel lost in Windows 8 because the whole thing hardly contains anything familiar to them. As such; Windows 7 is in favour.
But I'm pretty sure that whenever Windows 9 comes out and Microsoft has come back to their senses a little bit there will be plenty of people willing to upgrade to that.