I do not assume that. Google and Microsoft both do simulations of the visual page. It's often mentioned here that backlinks in the footer or a sidebar don't carry as much weight as links in the body content. That can only happen if Google knows something about the design your mark-up creates.
In addition, two years ago there was a thread in Google's own forum about a site getting a penalty because it was seen as having too big of an empty area (whitespace) on the page. In that case, the algorithm was wrong and the penalty was reversed. However, the message was clear - Google's algorithms do measure something about the design of the page.