In the case of the frame rates, the 23.97 and 29.97 frame rates are the actual frame rates. But most people just round the number up so that they don’t need to remember the point-whatever. But also, with NTSC, back when it was just a b&w signal, it was actually transmitted at 30 frames per second. But when color was added the transmission needed to be slowed down by point-zero-three frames in order for the color to work.
As for why camcorders have these multiple speeds is that some producers want the film look (especially if their target is a movie screen) or in TV production some producers might want to shoot at 24p and then create bot NTSC & PAL masters from the 24p master, just like they used to do with finishing on film (I.e. SeaQuest DSV). Also, even if the production is going straight to DVD, 24p is one of the video standards. If you have a DVD with a film in anamorphic widescreen from both PAL & NTSC regions, you probably have the same transfers as the studio probably put the movie on in 24p and then left it up to your machine to convert it to either 25i/p (PAL regions) or 30i/p (NTSC regions).
59.94 is rather recent, as it was found that with 30p recordings, the action didn’t look as smooth as 30i recordings, so the frame rate is doubled so that the action is smooth.