I think there are two reasons I'll probably go Pro. I assume, the Pro running a full version of Win8 Pro, can be joined to a domain. As such, I have access to my file server docs/photos/movies/etc.
As well, the Surface will be used by my whole family and so each person can have their own profile and can lock their session like we currently do on our Win7 Pro laptop. One of the things that makes an iPad and its ilk useless to me is that I can't put my email credentials or other personal things in without opening that access up to anyone who is using the tablet.