Go to www.idpa.com
and read the purpose of it. It is for shooting practical self defense scenarios in a "sporting" atmosphere.
The reason for the different divisions is for a level playing field. Unless your Jerry Miculek you cannot compete on the same level if you're shooting your Model 66 double action and someone else is shooting a single action Hi-Power.
To have any kind of organization you will have rules. If you can't live with the rules of IDPA, work to change them or just live with them. You will always have people looking for ways to "game it". I just go and shoot it as much as possible like I would for real and when it comes to others make sure they're abiding by the "spirit of the game", IDPA rules, and that they're SAFE...