OK, so the whole "Top Tier" thing was basically put together by BMW, Toyota, Honda, and GM and it's a voluntary standard for oil companies to meet. Maybe Toyota should have done the same with motor oils to avoid their sludge issues. But I digress.
A quick Google brings up many discussions about this, quite often contradictory and certainly anecdotal, inclulding this tidbit from associatedcontent.com (never heard of them before):
Left out of the Top Tier alliance, Ford has taken the unprecedented step of recommending a specific gasoline brand. Starting with 2006 models, Ford vehicles have "Ford Recommends BP" printed on its gas cap, which apparently includes BP's Amoco brand. It is not clear if this endorsement includes the SOHIO and Arco brands, also acquired by BP. In its press release related to Ford's endorsement, BP stated that it "backs up the quality of all its fuels with a written guarantee, and is the only major integrated oil company to do so." None of the BP brands are listed as Top Tier.
So Ford goes as far as recommending a specific brand while neither Chrysler, Mercedes Benz, Nissan nor apparently any of the French automakers seems to give a damn one way or the other.