Both headlights burned out tonight... Why?

[Green Monster]

Update:

I parked the Blazer last night. Came out this morning to check the voltage at the battery and at the headlights. 8.00V at the headlights and 8.15V at the battery. I turned the key to start the motor and nothing. No click. No crank. Nothing. The parking lights work and the under dash lights work. The radio does not work. The radio is an after market radio that is apparently tied into the red wire coming out of the back of the ignition switch at the dash. The ignition switch is original. I'm inclined to think my ignition switch is bad.

Is the bad ignition switch what caused my headlights to blow? Or is this just one over several things that has failed as a result of another problem, like a faulty voltage regulator?