I think men who need to be watched in order to even be able to masturbate make up an extremely small amount of the male population. I also think they are very rare on this site. Now, people who like to be watched are probably much more common.
That's a very fine distinction and difficult to quantify. At what point does like become need? I can't talk very much about this site specifically because I'm just a new member but even here every day I have received multiple requests to please watch someone just for a short while as they need to get off. (And need is the word they use.) If I went and sat online on more general sites this would increase 10 fold. Of course, I'm happy to admit that what I experience as a great deal of men may, in fact, be but a percentage of the whole. But its an active and obvious percentage in my experience.