"We have no plans to have in-game advertising in StarCraft II. We believe Bobby was actually referring to Battle.net, which has always included ads."
So StarCraft II is safe from this threat, at least for the time being. Good thing that Blizzard were fast in issuing their official point of view. Discussion were getting pretty heated in some corners of the web ever since this statement below was published:
"[Blizzard] has been thinking about how StarCraft, because it is a short-session experience, can actually be the model for in-game advertising and sponsorship and tournament play and ladder play for the future."