It's a commercial for the bike company's new 29er. They are trying to generate some buzz. Considering the fact the XC product is plain-vanilla 4130 and they want some sucker to pay $600 for it, they need all the buzz they can get because they aren't price/feature competitive.
The premise here is to generate buzz about the 29er. The wheel size for the guy riding the bike is immaterial. Have the riders switch bikes and DH buddy will still be falling over and generally falling behind. That would make a bad commercial though!
Nice trails! The guy riding in the shots is good.