OK, re-seeding for semis makes sense - semis are always re-seeded.
I'm not sure if the tradition is real or just perception. It seems like, traditionally, semis have been the two East vs each other and the two west against each other, guaranteeing a West v East final. The problem is if the two best teams happen to be in the same side of the state, one gets knocked out and you don't get a matchup of the two best teams in the final. So, seeding, regardless of geography for the semis, makes sense. BUT does it really? The big problem is there isn't a lot of common opponent information to leverage to make seeding decisions. So, probably just as good as any audience to have coaches seed. Can't think of a better way. Especially if they can use any information at their disposal (i.e. take rankings into consideration - or disregard them as they see fit.)