You know, I don't think this is "rewarding bad behavior." In my mind, at least, that is what happens when, say, a child has a meltdown and then a parent (or celebrity) gives in. Or someone waltzes in with unreasonable demands and expects to be catered to.
What Alton seems to be doing here is stating in advance what his preference is, so that everyone knows what the standard/expectation will be. Furthermore, he asks (not demands) that his preference be respected, and acknowledges that it creates some inconvenience for others:
"I will often ask that families with small children be allowed to come to the front of the line so that they can get out and to bed at a decent hour. This means some of you will have to wait a little longer. Thank you in advance for your patience."
Then he promises the "reward" for the good behavior, if you will, of respecting his preference:
"What I promise in return for this consideration is to never sit at a signing (so my feet will hurt just as bad as yours) and to never leave until the last fan has been greeted and their goods duly signed. I never have and never will (unless I have a stroke or something) left fans in the lurch."
I think this is actually the height of good manners, the opposite of rude, and pretty good behavior management while we're at it. I also think that it lets everyone know what the situation will be, so really they could plan. If I were to attend an AB event without my small children (if I could go anywhere without my small children, which for a multitude of reasons, seems like a fantasy at the moment), I might plan to arrive a bit later (say 20 - 30 minutes), or to browse a bit longer before getting on line, knowing that I won't be first anyway. I might get a coffee! And drink it in its entirety! While it's HOT! (sorry, the fantasy took me away for a minute