Google states that Google Public DNS does not permanently store personally identifiable information (source).
However, imagine that in the future "permanently storing personally identifiable information" is exceeding advantageous. So advantageous that even after taking into account the kind of bad faith they will receive from changing their statements, they will still make a profit overall.
When that happens, is it true that Google could simply revert their statement and issue a new contradictory one? Is there some kind of law Google will have to abide to, which prevents them from doing so?