the snowboarding link is good indeed:
- having both feet attached to the machine you ride gives you that "one with the bike/board" thing people rave about. I ride SPDs so it really feels like I'm attached to the bike.
- in both sports you can just cruise around and look like you're relatively good. Try that on a skateboard...
- fashion-consciousness runs high in some circles.. I can't think of a sport where kids HAVE to have the coolest gear every season more than in snowboarding.