“On TV, content flows like a stream. Miss an episode of “Friends” and (assuming you’re not a member of the TiVo clan), tough luck. When something unwanted comes along (like an ad), it’s perceived as part of that stream. Viewers understand nothing’s lost in looking away until “their” stream continues. They dislike commercials yet forgive commercial interruptions.

Online is different. Content’s always present, always accessible. When an ad is onscreen, even just occupying space where content could or should be, it’s perceived as being in the way of the experience. TV spots are much more intrusive but are seen as less so, because of the way people feel they should be able to experience the medium.”

Gary Stein, Forced Entry: The Intrusiveness Question