If you adhere to the narrow definition that waterfalls must actually be free-falling then yes I suppose most waterfalls would have to be plunge type waterfalls. But since there is not a universally agreed upon standard that stipulates that in order to be considered a waterfall it has to be a sheer fall, this isn't necessarily correct.

I'll also point out that three of the waterfalls on EG's list in the link are not true plunge type waterfalls.