Wow, I didn't expect only negative replies so far.
Seems to me that we, the American People, are already providing vast subsidies to the airlines. In return, isn't it reasonable that we ask the airlines to provide what would otherwise be empty seats to our military at advanced purchase rates - not a below cost cut as everyone seems to imply? I don't think the Mom's are asking for below cost here, just the same break as if the soldier knew about the leave 30 days in advance.
I don't purport to speak for the Mom's and I'd have to think they know about the other programs. Maybe it is a space issue or the fares aren't discounted to the extent that 30 day purchases would be.
In addition, I think the post-9/11 security has pretty much done away with stand-by. Not to mention the airlines tacking on $100 penalties for a ticket change.