I would hope as sparks, the risk is obvious? For the same reason there are rules about zoning in the bathroom, around the kitchen sink etc? Because the 2 don't mix.
Picture it; G&E meters both share a cupboard, said cupboard is near other cupboards that are used for storage, a good forgetful throw of something into the G&E cupboard and you have a loose regulator/isolator. I would say that's far more likely to happen than electrocuting yourself in the bath but then again; stupid is a stupid does..