Every camera captures more colors than what appear in smaller spaces when shooting raw and thus all can take advantage of ProPhoto.
Yes, if you shoot in RAW, and bring a shot into Photoshop using ACR under ProPhoto, you will get access to the full range of color detail produced by your camera. But your display or output devices may have much smaller gamuts than the ProPhoto space.
I think that may be why some people avoid the wide gamut editing spaces. Since they can't see any difference on the monitor (or even with printed output, unless all the correct color managed details are handled correctly), they assume there's no benefit. But if you watch color numbers carefully for specific pixels while editing, you can see huge differences in the ability to make subtle corrections. In my opinion, this is one of the major advantages of RAW capture.