Incidentally, for anyone else curious, I stumbled on the OZ RTW fare. You can get a significantly cheaper *A RTW fare ex-London on Air New Zealand. Their fare is about 1,050 GBP a.i. or less than half the *A fare.

You can actually make it all the way around the world on entirely OZ. If you add in any United legs (but you can't add arbitrary *A -- it won't get me to Canada ) they seem to add to the price, I'm not sure exactly how its calculated.

One thing that's annoying though, it's significantly more expensive going West than going East. I suppose most of the flights are in the northern hemisphere so they take longer going that direction?