IE 10 differences between Windows 7 and 8
msdn.microsoft.com
msdn.microsoft.com
So they should be able to implement their API on win7, since they're suggesting others can (and should) do it on pretty much every OS out there.
Doesn't make a lot of sense once you write it all out.
The problem with this explanation is that the purported advantage of the Pointer API over apple's touch API is it being "pointer-agnostic", it's supposed to unify mouse, fingers, stylus, etc... events into a single coherent one. So implementing it on non-touch devices (which isn't the case of Win7 anyway) would very much support its integration.