Supplemental, of course, because it obviously isn't the most scientifically rigorous data. Notice how at one point they ask if you're willing to take part in more in-depth case-studies? Yeah, that's a part of the more serious side of it.

EDIT:

Some of their assumptions are really flawed though, as much as I support their work. For instance, they lump online multiplayer with strangers and face-to-face multiplayer with friends into the same category, even though they are wildly different experiences with wildly different markets.