I must say that I do know some people who use skates for transportation. It's not their only mode of transportation and not even primary mode of transportation if you look at it year-round, but it is their main fairweather way to get around town. I'd say it IS a real transportation tool but it's limited in many more ways than cycling.

It also requires more training and greater skills, I would say. The absence of a real reliable brake that doesn't wear out at a ridiculous rate is the main reason I don't skate more even in good weather.