To my understanding, the reason why webmaster didn't put any house rules/modification of the original board game version is a kind of respect to the original Author, and also they wish if inspired user (by the online version) would buy themselves a copy of the game.

I belief that Nick/Fourth wish everyone of us to promote the boardgame (paper) version in real life. When you have your own copy, you can modifiy/change whatever you like and enjoy plane simulation with friends and love