Noggin- although RPS is not ideal for avoiding controlled airspace it is better than b*gger all. Iddeally, everyone has an IR, flies IFR in receipt of an air traffic sevice and flies high enough in their FMS equipped jets to all be on 1013.
Yes it is flawed but it is still better than nothing when operating OUTSIDE controlled airspace latterally and if operating UNDER controlled airspace you should be on something more appropriate or giving a good 1000' plus clearance. If I remember correctly (and I don't have a chart handy), most airways have their bottom level defined as a flight level so 1013 is a good setting. If they have an altitude as bottom level then RPS with 1000' should do (the RPS is unlikely to be over 30mb off the actual QNH/QFF).