Not nearly as selective as the cases that end up on Hacker News, i.e only cases involving large US corporations.

The commission and national (European) regulators are investigating ~150 cases every year, most of which none of us will ever have heard of.

http://ec.europa.eu/competition/ecn/statistics.html#2

The ones I know about have all been the result of a complaint made by competitors. I would be surprised if the regulator could selectively reject such complaints without good reason.