Atlas, thanks, that's very interesting. Two questions, if I may:
(a) Why 1,500'? Is that height significant, or is it an arbitrary point?
(b) Why "alternate fuel, but only if you can't manage (5)"? Surely you must always provide for diversion to alternate – from anywhere, down to GA after touchdown – since many things beside WX or ATC holding can prevent you from landing at the last moment?