"Isn't the gathering bunker somewhat incompatible with the hairy bunker that is the current rage? The hair keeps the ball from funnelling off into the sand."
I believe this question by John Cullum is a very important one--probably the most important one. Of course drainage and surface drainage is important to bunkering anywhere but we can certainly see in Europe that in many ways those bunkers on links courses are going to get rainfall either in them directly or as some result of sheet drainage--like anywhere else.
I think the major difference in the effectiveness of European bunkers to gather balls into them compared to their American counterparts has to do with agronomics and the maintenance practices thereof as John Cullum's question suggests.
We certainly can't help missing the fact that the most effective European gathering bunkers (Troon this week is a perfect example) are basically revetted bunkers with extremely close cropped grass (akin to a very close cropped chipping area) completely surrounding their every side. That's definitely an agronomic and maintenance issue which makes gathering golf balls into them far more effective.
American bunkering (some of Steele's North American work being the exception) is generally far more grassy surrounding both the incoming and out going sides of bunkering! As John Cullum's question suggests, and my own super implied---how do you meld the grass cuts around bunkering if one side is shaggy and the other isn't? (Actually the last time I saw some of Atlantic City C.C's fairway bunkering, it could be a perfect example of how to do that---with a lower cut on the fairway side of the bunkering and higher grass on the rough side of the bunker!)
I did a study of the surrounds (grass) of bunkering of American courses using some of the old photos on a number of old American Ross courses and it appears in America even in the early days bunkering always had higher grass rings surrounding it, although, in some of the early photos it appeared shorter than it generally is today.
But again, this is a question of agronomics and maintenance practices as it relates to the ability of any bunker to "gather" balls effectively into it! (This may also have to do with the old agronomic cliche that in America they're always trying to get grass to grow while elsewhere they generally try to stop it from growing!
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It just appears we in America have always done this differently than they have and continue to do in Europe and on golf course elsewhere such as the sand belt courses of Australia! There's little question that the far greater ability of European and Australian sand belt bunkers to gather balls into them has to do with less and far lower grassing around the bunkering surrounds, not necessarily some architectural difference (although revetting is far more common in European and courses elsewhere than it is in America).