Airsoft is a hobby not a job. I have hosted games before, and people who back out are frustrating... but real life has to take priority over a hobby for a healthy well adjusted adults. School, work, and family commitments should always trump play time. I will agree that people should be able to manage time effectively enough to not have to back out, but many commitments such as school and work don't give you notice that far in advance. If you want people to post "in" a month or two in advance, expect alot of variation. If you want people to be 100% sure, expect alot of last minute sign ups. I think it's unacceptable to remain "in" then simply not show up to the game however, and if you have to back out you should give the host as much lead time as possible.
I think your game had alot of people back out (including myself) because you were asking people to commit two weekends to one airsoft game. I would rather take a for sure game than a tentative one. I would have been able to play at your first date, but I am not going to reserve two weekends where I could for sure play at another game just to keep it as a reserve day. If youre going to host, pick a date, and do it rain or shine. If you really really dont want people backing out, ask for deposits. Just dont be surprised if you dont get 80 people.
"Hokey religions and ancient weapons are no match for a good blaster at your side" - Han Solo
Commanding in Airsoft