Let me say up front I'm not a member if IDPA, though I admit my interest is piqued. And I think I understand and agree with LEO's and Mil using their issue gear, as it's what they regularly shoot with. Though if this is a competition, I can see where such rigs would have a distinct advantage in draw speed.
As an "outsider" to the sport I'd like to ask a question, if it wouldn't be toof ar off topic:
If it's about (primarily) civilains using CCW gear available to them, why are cross draw and shoulder holsters not allowed?
Both are legitimate CCW options for a civilian (as well as LEO and Mil for that matter in the right circumstance).
I'll have to look further into this sport.