From a corporate point of view as well there is a big cost for training users to work with a new OS. XP to 7 was a big leap for a lot of non tech savvy users and the UI was not that different. Jumping to Metro is a step too far for a lot of businesses.
As well as that many software companies don't release updated versions of their software for months (if ever!!). We are still regularly told that x software needs Java 6, IE 8, Win XP to function properly it is a nightmare!
The old spoon fed and training argument,personally if they can't use Win8 (which is damn simple and I say that as a 50+ year old with no PC training even when I was at school for obvious reasons).
As to training argument sure it costs but then you can't expect things to stay the same forever in business etc,hiring smart people or workers capable of doing the job,willing and able to adapt keeps your costs down ,lets face it you don't need a degree to click a few mouse buttons here and there.
I could argue it does not take long for any user getting to know Windows 8 or any other OS if you are not lazy and willing to learn,its not rocket science or beyond any average persons means.
You have to learn and get to know any OS regardless,it could be Win7 for the very first time or even Win9 etc...
Win8 is not that different from Win7 and I've purchased and used both from day one.
People don't become suddenly stupid because layout or OS has changed.
I can understand keeping costs down but don't corporates have to spend on training,research etc to compete with other companies.