Guys buying new high grade guns overwhelmingly select the small gauges. Just look at Galazan's new guns over the last few years---all offered initially as small bores. They are just fulfilling a market want/need. The same holds true in the vintage gun market----small bores rule the top of the market. I think because small bores were so few in number historically, the purchaser of a new high grade gun feels like it will add to it's exclusiveness if it is made as a small bore. I don't believe the killing efficiency or effectiveness is a big factor in this type of purchase. Many of these new high grade guns are for show not go.
For waterfowl hunting and wild pheasants the 12ga will never go out of style---they are just the best tool for the game.