Whilst not a deal breaker, I think it is important that you understand how things are built on the web. Especially knowing how to fully code in html. The more web programming you know the better, and working closely with the dev team has constantly reminded me why this is important. There will be plenty of cases where being able to understand a web development language will be very advantageous. When for instance, the dev team says there is no space for particular piece of content , recommending a work around using a CSS overlay and calling it using an onClick event maybe accepted. Or telling them that how best to code in Google's language alternative tag across an already existing international site.