The Surface is a strange one, seeing as it is both a PC and a mobile device in one. There are upsides - as you've mentioned - but downsides too. I suspect my parents might not be quite as comfortable using a Surface than they are with an iPad. I'm glad your wife is enjoying it, though.
However, I'm really not trying to get into a war between platforms. My point is that adding limitations, which many of us see as reducing how powerful a device is, can actually enable the user to go further and do more than they could previously.
So yeah, mobile is limiting but it doesn't have to be. Once you venture outside of Apple's cold embrace, many things are possible.