prototypes, marketing, and testing, it's that simple.
Prototypes are made of next years model so the pros get them to ski as hard as they can, if anything goes wrong with the ski they can tell the guys who make the skis to get it fixed.
Marketing is simply so WE know what to buy next year, think about it, the first time I was Line Afterbangs was in Traveling Circus and that's when people started to say "I want A-Bangs". The pros ski them in advanced so that they can show them off
Testing is simliar to the prototype thing, but this time its with the final product so they can give reviews for magazines and stuff.
It's just a perk of being a pro.