Numerous eye-tracking studies, done by multiple large research companies (many of which having been researching website usability for a while), have shown that, though humans are sometimes attracted to graphics, they also
- are first drawn to text (78%)
- spend way more attention on text (many times more, judging by the eyetracking heatmaps from the studies, linked to from this article)
- remember and can recall more textual information, than otherwise
Of course, all those thorough studies have many more points to add. Let’s look at them a bit more closely.
Read the full article at ImproveTheWeb.com
Of course, the ad position inside or outside of the top-left triangle plays a large role. But the post was more about casual images and graphics that are not related to page context.
As you have observed, non-contextual graphics/images are ignored, too.