I can confirm this. All web projects I worked on which were minimalistic, clean and well designed had less stickiness (page impression count to visits) compared to sites stuffed with content, pics, links, extra widgets here and there.
No citation is needed for an unactionable assertion. Do you really believe in the entire history of every web page ever, this is untrue? The statement was more or less tantamount to use metrics to make decisions.
Oftentimes an ugly site with ads and popups everywhere will perform better than a beautiful, minimalist site. Sorry, but that's just reality.