Windows RT tablets with 3G support ?

I guess we haven't see a Windows RT tablet with 3G support.
Is this because of Microsoft restricting the OEMs or just that OEMs don't see this as a profitable usecase ?
I was able to find even Windows 7 tablets with 3G support, hence its technically even possible to include 3G support even in the Pro versions on Intel architecture.
Wouldn't it be more sensible to include 3G support and provide a options for users who would want always on connectivity, rather than just rely on Office/Home/Cafe WiFi ?

Also theoretically if Windows RT support 3G bands then we can see Windows RT in phones too !!! Perhaps we could see some phones like the XPphone.