Sure they don't.
Also this is not impossible to write an unpacker... The driver should only gain the lowest control, it don't need to be full of procedures - I see using this level only for initialization, then giving back full control to main thread. Most of the people are scaried with XProtector because SoftIce extensions doesn't hide this debugger - Then legends about XProtector are being written...
Syd (Stripper author) was the first one writing efficient ASprotect unpacker with device driver routines. And I have a big respect for him for that.