I think BA/AA/Oneworld actually used your case when American and British Airways tried to get US Antitrust. Last time I checked, Lufthansa and United have a stranglehold on the US-Germany and Central Europe markets and the reason British Airways serves so many US cities(for which Capitol Hill should be thankful for as if it weren't for BA, many of those cities would not see trans-atlantic flights) is because they have no US partner to feed to. To make things worse I think UA/BM received Anti-trust immunity. Another example is Delta/Air France, the two of them have a stranglehold on the US-France market. Take NW/KL, they probably have 90% of the market for US-NED flights and the government is totally blind to this. I couldn't agree more with you. You brought up a great point.
Regarding AA/LX, I think that alliance is actually expected to get anti-trust from the US government.
I think a lot has to do with AA, for whatever reason, the USA and Hong Kong do not have open skies and AA/CX have been pressing for an alliance for years and are just now expecting to get approval.
I'd say it's time for the US government to give AA and BA a break and make things fair. Also, I think that is the main reason Oneworld sort of lags behind. If SWISS joins Oneworld, this might ease things up a bit, and ZRH would become a great Central European hub and reliever for LHR(along with DUB/SNN with Aer Lingus)
Give me a break, I created this username when I was a kid...