In this case, the gentleman's behaviour helped resolve the issue because he got to recline and you got to sit without him in front of you. Much as we like to criticize asshole behaviour, it can be be very effective at times.
Explanation as to why siblings are such jerks to each other? Because parents have the ability to intervene and provide more resources?
Ultimately, the instigator of such a request should have used a more polite way of making his/her request - just like we ask our kids to do. Because at some point there won't be extra resources to shift around and then the situation escalates and someone gets hurt.
Flight attendants and many other customer focused workers learn to triage. If you make a polite request the chances are that you will continue to be polite and so become a low priority. A situation like mattezell described has the potential to spiral and draw in other passengers or cause complaints to be raised. Thus the attendant has every incentive to mitigate the situation even if it comes at a cost to more polite passengers.
