Today US rating agency Standard & Poor’s told a court of law that it figured every reasonable investor would know its promise to objectively rate securities was mere “puffery,” like a used-car salesman who tells you the last owner of your car was an old lady who only drove it on Sundays.

The US government thinks that S&P (a unit of McGraw Hill Financial) should pay $5 billion in penalties for giving safe ratings to risky securities while it had cozy relationships with people creating them. Somebody should have known that all those chopped up sub-prime mortgages did not actually create bonds as safe as Treasurys, and it turned out those somebodies were helping S&P create the models that said they were safe.

Moving to dismiss the suit in a California federal court, S&P said that reasonable investors would know its assurances of independence were just marketing, and that its ratings should be treated as free speech, not as financial statements. The defense ought to worry anyone who relies on its ratings. But should the government win this case, those investors will likely file claims for damages in civil court alleging that they too were defrauded.

Beyond that, the whole industry of rating securities depends on the idea that ratings have some analytical value. This defense suggests that securities ratings are more about marketing, and indeed, the market has tended to ignore some recent sovereign downgrades issued by the agencies. The US government is trying to strip ratings from the legal code so that its financial decisions won’t rely on them. But it’s not likely to fundamentally change the market by, for example, selecting the rater that a securities issuer uses randomly from among the accredited options.

In the meantime—if you’re not already doing so—we suggest you take your AAAs with a grain of salt.

Update: The Wall Street Journal is reporting that the judge has denied S&P’s request for a dismissal for now and will allow the trial to proceed.