[quote name='Nadie' post='1294746' date='Mar 31 2008, 11.00']Ah, Ned would have done the same thing. Say what you will about him, but he was dead serious about the Wall. The very first chapter we see him in he beheads someone![/quote]
Not just the wall, but pretty much any serious laws of the kind. His opinion of Jorah, for example, he made it rather clear he was going to behead him, and would still do so if he fell in his hands again.
So, yes, what Jon did in this chapter is exactly what Eddard would have done... but he would not have had to, because no one would have dared defy him like Janos did. And that's the whole point Aemon is trying to make I believe.
Eddard had already proven he was more than willing to enforce his authority, as I am sure the Old Bear had as well. Jon, however, still hadn't proven to his men that he was capable of making the hard decisions, and he remains a child in the eyes of most (including Janos, obviously). By justly enforcing his authority, by hanging one who disobeyed and defied the direct order of the duly appointed Lord Commander, Jon proved he was ready and able for command.
Or some such. :)