Godaddy does not write anything permanent to my CSS or html, I think that while the server is reading and building my site the advertising is inserted.
They do talk about how pages built with (non movable) div tags can be messed up by not allowing the advertising to just push its way into the top, other wise things end up on-top of each other - a mess.
I'd be so sweat if it was a tag of some sort that just loaded a banner, so much of Joomla fails because of it, and I reckon that they know about it too.