“So why should that limit be eliminated before LHR gets opened up to any airline that wants in?”
I agree that everything should be equal. The problem is that if you wait for that, you will be very disappointed. The world is not perfect.
This is the same principal as trading with China, which is not fair. The downside of not trading is very bad.
Continental is supposed to be starting LHR service in the summer of 2008. Let Virgin America start service then.