Net of all and back to the OP original question:

- you probably can get by without them in DC
- you very well might be wasting your money
- studs aren't going to do much in the snow. Honestly, even with studs, I don't like to ride in the snow. It is too much work.
- but if your commute, like mine, has significant amounts of ice that lingers for many days after the normal snow & melt, AND the cost of the tires is worth those extra days of being bike-capable, then get them.

As long as you have a plan B for your commute (Metro, bus, car, slug, whatever) I'd recommend NOT getting them until you find out what the ice on your route(s) is like. Spring for them mid-winter or before next winter.