Kikolobo - I think one problem is that the RoD figures used to define the conditions required for VRS haven't changed in 40 years (maybe more) from when helicopters had low disc loadings and therefore low downwash speeds. Add to that a safety margin and, as Nick says for the R22, the bracket starts at 700fpm so if you always react at 4-500 fpm you will pretty much be safe.