Example: The demo site uses Proxima Nova, which is loaded via Typekit. That's not an open source font, there's nothing documenting that they have a sublicensing/resale license, which means it's an added cost to someone to either license each weight of the typeface ($29 per weight, and I think I count 8 weights = $232). Alternatively, that font is only available in the Typekit $49.99/year plan, which imposes pageview limits. The typeface really seals the deal and adds to the emotion of the page, and could be a big disappointment or added cost to someone. Certainly, startups don't need the drama of being accused of copyright infringement.