Zauron
Smash Journeyman
No, in many cases the videos show a player's hands. I've watched their hands to see what they are doing. They aren't pressing L or R to cancel their air attacks when using the classic controller. Its harder to see on the Wii-mote, but if you watch it with frame advance you can see how their hand grip changes when they press the B trigger when they block. They aren't doing it when we see air attacks land that look L-cancelled.The people playing the demo may be pressing L out of habit. I do the same if I'm going to shield/dodge immediately after landing from an ariel.
There's no way to tell for sure until someone tried this out specifically on the demo - even THEN it's questionable because IT'S A DEMO.