I too would have probably preferred to see Hall at Boston, but given the talent pool in London this year, it was probably a better lesson race for him leading into Bejing.
I could go either way on that. I understand your point but Boston has more in common with an Olympic marathon in other regards. Not having rabbits, it's more of a championship-style race (though this year, it sounds like the rabbits didn't do all that good of a job making London a time trial-style race). Also, typically, the Boston conditions are more similar to an Olympic race than the London conditions are, though the conditions in Berlin could be so severe nothing will prepare anyone for what is to come.
This could be just like last year, though. Getting out of this country allows him to fly under the radar a bit more, which would allow him to maintain his focus better on what really matters.