I actually completely disagree. I don't like the approach of speccing out a feature and just having someone else execute. We are a startup of around 25 people with only a few devs and one designer. We don't have the luxury of doing multiple mockup iterations, perfectly speccing it, and getting someone to do CSS to match the pixels.

Saying CSS/HTML are just pure execution completely undersells the complexities of user interaction, the changes that happen when a design actually becomes interactive, and the feedback you get from your team as they start using the prototype.

I usually am simultaneously mocking things up and coding the initial prototype, and then we iterate on the prototype and a lot of decisions are made during that process that can significantly change the feature. We don't have the luxury of having something finalized/tested/specced before building it. Design and development are essentially one team here, and they are a lot better for it.

I find a lot of discussions about web development don't take into account small startups with limited resources. We have an enormously complex and polished web app and we do it without any of the crazy number of steps other people go through.