I think they only request them to be removed if they are impacted. If the teeth are erupting at an angle, it puts pressure on the other molars and may cause pain or crooked teeth. Also, if the tooth is only partially erupted, they "claim" food and bacteria are likely to collect around the impacted tooth causing problems.
My dentist told me that my lower ones would cause problems, but the upper ones were fine. I could see on the x-ray that they were coming in at a 45 degree angle, so I had them removed. He didn't pressure me; just informed me.
I'm not defending him though. When I asked him about replacing my amalgam fillings with composite, he got extremely defensive and basically said it was bolgna that they were harmful and natural dentists are just out to make a buck. After that, I never went back and haven't been to a dentist in 3 years.