While I agree skiing indoors isn't a good idea, it does allow you to reduce the tedium of taking them off and putting them on again as a player. It can also be noted that you can't run while wearing skis (unless you engage in exploits), and the skis weigh a fair bit, so I wouldn't bother to code the further penalties that ought to be on top of that.
(Those who say you can't ski without snow haven't heard of the Finnish skiing athlete Juha Mieto, who was said to be at his comparative best on rain slick asphalt, only half jokingly).