It is not AI. The NPC creator was too lazy to add a new line of dialog and conditions... :/
It could be that the lines are there, and that the triggers/conditionals are not properly set. I mean, everything else seems to have reaction dialogue, like simply joining the Companions. It just seems that they are messed up for the Mage College.
Not sure if you can look for dialogue lines without the Creation Kit, but if any of you uber modders out there who can mod without mod tools can find out, it would be appreciated

@ Frotality: They did the same thing in Oblivion. They would randomly react to your armor, your skills, and your guild associations and they would do it more than just once. The difference here in Skyrim is that, for some reason, no one acknowledges anything pertaining to the Mage's College, yet they react to your status in other guilds. Even the DB has the occasional guy who will say, "Hail Sithis!" when you pass by.