I agree that designer’s should look outside of their own domain. The illustration, print, UI and UX work on dribbble provides a good sampling but certainly isn’t all inclusive (but then again, this article was only about dribble itself).
I would disagree with statement about monoculture. This is only one designer’s homepage and it will evolve over time as the designer grows him or herself. Being able to curate your influences is healthy in not only establishing your taste but helping you find opportunities for differentiation.