As I have understood it, and correct me if I am wrong. It is all a matter of perception. When I was visiting Germany, bartenders refused to serve beer with out head, they would actually pour some beer ahead of time, then top it off to ensure good head (it would only be a matter of minutes between filling and topping.) I was told that the head gave aroma, which as we all know is essential in beer. In the UK, and other such places, they want to ensure that the volume that they are getting is the volume they are getting. Of course this may just be one side picking on the other, but that is what I understand. Personally I prefer a nice head on the beer, not too much, but one that will impart the aroma.