Dick -
As other posters have said, we have been using those definitions for years. If I think I am going to land below Final reserve (typically about 4.2 Tonnes in an A380), I want ATC to treat the airfield exactly as if I have an emergency. Eg, tell Aircraft in front of me to go around etc. Because if I have to do a go around, a typical go around, and return to landing will take about 15 minutes and 3 tonnes. That would definitely have you sucking the seat covers into your butt cheeks.