How did you know it wasnt your speedo head?
You are lucky, if you think about it most people would just remove all the stuff, and take the speedo not go to the trouble of fitting another.
Wouldnt you also have to remove your head light? Isnt the wiring down to the wheel contected to it as well, I have one but cant remember?
Bad luck, what is the world coming to, was the bike at the pub like crash said, didnt you lock it in the laundry like normal?