From my experience all glider pilot know the rules of 1500m Horizontally, and 1000 feet vertically above 3000' AMSL or 1000' AGL whichever is the higher. It is certainly part of the oral examination here in Aust. However realistically most glider pilot get alot closer than that, however all (unless idiotic) do not actually get into cloud. On somedays with low cloudbase you would be able to do little else if you maintained a perfect 1000' from cloud. Although technically against the rules, its arguable as to whether it is dangerous provided certain precautions are taken, the key one being a good look out and listen on radio for powered traffic. If it a day with complete overcast more distance would be desirable as compared to a day with scattered cloud where you'd be able to see the traffic inbetween clouds. Also avoiding NDB let down area's in cloud.
To be honest has this ever actually caused great distress for you? or caused a near miss? If not then why the bitchy attitude?