Why have the Jerk British judge?

I've always wondered why in recent times (last 5 years or so) that ALL of the US reality/talent shows always have that one bad guy British judge, the prime example being American Idol/America's got talent. It is always the British judge's job to be the bad guy and critic. It just boggles me. Why can't Americans take critisism from their own kind. Maybe it has to do with ratings and such and how being judged badly is less embarrasing coming from the mouth of an "outsider". To me it just feeds the stereotype of the uber-preppy and sofisticated brit. Kinda like the french stereo-type. I just wonder why can't networks have people being judged by their own kind. To me it seems like an insult having an outsider of culture telling what is wretched and fabulous in front of my own people. Gosh Darn Brit! Who judges their reality contest?