This is incorrect. I used to use Win7 on my laptop and if I used internet connection sharing it used to create an ad-hoc network and if I wanted to connect to an ad-hoc network it was the same too.

I've read on Win8 being slightly more difficult to create ad-hoc networks so I'm sure if the tablet is a Win8 Pro not RT there must be a way to connect to ad-hoc networks via some obscure method...

Not too sure if Win8 RT supports ad-hoc though I'm pretty sure just like Android devices having work-arounds to allow device to connect to ad-hoc there must be some work-around for RT too...