Of course, this begs the question: why can't developers just install the code themselves? Ostensibly, the demands of the advertisers give developers a monetary incentive to improve on the existing design and architecture of their game that they might not otherwise have. In an ideal world, making their playerbase happy would be reason enough for developers to get things right the first time, but in this cynical world we live in, I guess that's just not the case.
Still, whether it streamlines the design or not, we're still going to bitch about seeing ads in places where they don't fit. See: the above image of a Dell XPS computer housed in a tent on the tropical planet of Foreas in Tabula Rasa. I always pictured the Foreans being Mac users, myself.