Studded tires are really not necessary around here. I commuted years without them. In fact, I've ridden to work on slicks on when the whole DC region was shut down by snow and ice. As long as you just coast, don't turn, and stay off the front brake, you can ride just fine on black ice. However, riding in slick conditions takes a lot of skill and is mentally tiring.
However, studs make life a lot easier. No worries when you are are work and snow is falling. Riding on ice is like riding on a wet road without studs. Riding with studs on glare ice is a smooth, dreamlike experience -- it is like a big ballroom. You can use an unplowed/intreated bike path as a shortcut. There clearly are safety benefits to having the best traction of any vehicle on the road on an icy day. So I put them on in December, take them off in March, and just leave them alone in the meantime. I'm maybe 5 minutes slower getting to work when roads are clear, but it could save a half-hour to an hour when they are not.
I also think Metro DC has less effective plowing and treatment than Baltimore. You don't hear about everything in Baltimore shut down for days after a storm.
Studs are about like knobbies when it comes to rolling resistance. If you have to have knobbies, I figure they might as well have some metal in them. On my bike, there is no noticable rolling resistance penalty when I mount just front studs. However, I live on a hill, and no rear studs meand having to walk the bike up the hill -- not easy, when walking is hard.
Conclusion: find out what works for you. Studs all winter works fine; all winter without studs works too.
Paul