Rather than make broad claims like "pretty much all"... if you took a little time you might quickly realize which kind of drivers work and which don't.
I'll give you a hint... plug in a USB webcam (even one from Microsoft) into a Windows RT device and see what happens.
Allow me to save you some time: No driver will be found and you won't be able to use it.
Does this mean we have a conspiracy not only to kill off Ethernet but also external webcams?
Clearly the "big monitor" lobby got someone in Microsoft, just like someone from "big-wifi" clearly got in in order to try to kill competition in a rather silly way.
Blowdart said exactly what the reasoning is for this, sorry you don't want to accept facts.