These are based on the the American Society of Magazine Editors guidelines for the relationship between editorial and advertising in print. The dynamic technology of electronic pages and hypertext links create a high potential for reader confusion. Permitting such confusion betrays reader trust and undermines the credibility not only of the offending online publication or editorial product, but also of the publisher itself. Brand is worthless if I can't use your site. Ease of use is more important than brand.
Ease of use brings readers back.
I have to wonder if one of the reasons we aren't seeing style sheets take hold is that by intermingling content and structure, that sites beholden to advertisers make it that much more difficult to do simple filtering to remove ads and other noise. If you want to make money off your site, then work towards getting micropayment systems developed. Advertising types get it with respect to the risks posed by merging ads and content on Web sites. If you blow their trust by letting advertisers dictate content, they may go elsewhere. And on the Web, unlike TV, there are many choices.