I took my thinking about this a bit further but posted it to the main BrainKing board where arpa raised the issue.

It's serious: This change will have a severe flattening effect. If left alone we will all - high and low - eventually have the same rating!

http://brainking.com/en/Board?bc=1&bscx=403725

(Bear in mind that the link puts my message at the top of the page but doesn't show anything posted afterwards. There may well be replies to it on the "previous" pages.]