I agree with this article, but who is to say the goal of Dribbble isn't to just showcase visual design? To join Dribbble, you must get an invite from a Dribbble user. Dribbble users invite people who have similar taste and design state-of-mind as they do. So in the end you get a gated community of designers who think and work alike.

The problem with this I see is that non-design people who wants to hire designers think that Dribbble is the "go to" standard of design, without thinking of usability problems their product[s] have that needs solving.