Please help me figure out how this works...

I'm trying to figure out how, with far less than 15% of precincts reporting and a very slim margin, they were able to call it for Lieberman. If the exit polls are not used in this formulation, then what is used, and if the exit polls are used in calling a race, then how come so many politicos here discount them? It seems to me very contradictory. Please help me understand. Thank you.