Having ammo would add another level of gayness to mini-games, Oh I ran out of ammo
* Packer goes to pick up ammo
* Packer get spammed to death by ammo campers
For some things it'd be good but in general death matches it'd suck and you'd be better off killing yourself.
Well, its a double edged sword.
One one hand, with ammo, people could camp the ammo as you said, however people will know that he/she is camping there and can respond accordingly.
On the other hand, without ammo, the player is free to spam his/her weapons where ever they please for as long as they please.
I'd prefer to have ammo, perhaps limit the amount that can be carried (EG. Rocket launcher only holds 2 shots).