yes, there is a difference but really just semantics. you can have 30 on the "team" but the coach will have to name the "roster" for each and every competition. it can change week to week based on things like injury, sickness, family death, etc; and this and below apply to the women also.
some of the colleges "limit" exactly how many can be on a team from the full scholarships, to partials to walk ons. what the school does has nothing to do with the NCAA. the limit is "12" for the women on full athletic scholarship. the most for men at any given school left that has boys might be 6. i have not heard more than 6.
like i said, my colleague is not sure what your mentioning about the number "15". and let's say it is 15, they won't all compete all around. this applies to the women also. and my colleague says he doesn't know anything of a "19" rule but that it might be a title 9 issue but does not apply to gymnastics.
and the 30 guys thing. remember that there are only 14 D1 mens programs. so if club has a bumper crop graduating class, you could find that many on several teams because they only have a pick of 14. unlike the women which have a pick of 88 (i think that was the last number i saw).
as far as college club, these kids seldom will be on the regular team. they have their own competition schedule with regionals and club nationals. it's a whole different ball game.
and as far as budgets, all the schools are different. some will only allow a couple of walk ons. but look at Iowa mens and women. they have a lot of walk ons. more than most of the schools. and i suppose this can be an advantage. if most of the team goes down with the flu they have many to pick from to field a team.
