A/B testing doesn't necessarily mean "test two subtle shades of the same thing." For a great example, see the Highrise A/B test: http://37signals.com/svn/posts/2991-behind-the-scenes-ab-tes...

This is a good example that disproves many of the false premises mentioned in the OP, as the clear winner of the A/B tests was a bold dynamic design with lots of character, that was completely different from the original designs.