Nice post. One hypothetical case it could end up serving the worse design more often is if you had times of the day where your users behave very differently due to time zones, i.e. Europe vs North America.

Say you have a sports site and test a new soccer oriented layout vs an old baseball heavy one. In the day, the old baseball version wins easily. When NA goes to sleep it would serve up baseball to the Europeans until it loses, then after several hours soccer is the winner. But then it is too late and the Europeans go to sleep and on and on. This is an odd example and assumes equal balance, and the site should really be localized, but you get the point.