My guess would be those newer to the scene or that aren't real experienced with arcade emulation lump them. Those that have been around a while and understand the hardware differences (or set differences) probably then start going down the road of splitting some of them (especially ones that need an emulator that isn't MAME). That being said a LOT of users also still have no idea what each type of MAME set is and how they differ from another so many things like this we really have to straddle the line and play nice and work well for both camps in this scenario. Not saying there isn't room for improvement in the situation, but this is the type of thing we run up against with some of these features.