Just because we're building bad-ass infrastructure and tools doesn't mean it can't be cool, stylish, and fun. Aesthetic matters. See The Substance of Style
Slick and fun meets powerful and serious.
Before Heroku (and a few others, like Github and Atlassian), developer-facing products were almost always stodgy, ugly, and completely lacking in style or fun.
We're part of the consumerization of IT.