You're probably right that it's both. That said, you can nuke these with CSS. I've taken to pretty liberally modifying site stylesheets (I've compiled almost 700 of these), and nuking things like interstitials, "social" toolbars, "related content", slide-outs, etc., is high up my list. A few of those are now in my default CSS (the Tumbler teaser most notably). Pretty easy to do using Stylebot (Chrome).