Yes, the government is taxing per a gallon, so the more gas per a gallon costs the less per dollar of consumption they are recieving.
But in actual taxes collected per fill up, that hasn't changed. People are using more gas in this country all the time. Studies have shown that despite the carpool lanes, buying up of hybrids, etc, people are still using more gas collectively than the year before, and the year before that. Look at the cars on the road. The majority are still big SUVS and personal trucks, loaded with only one person. We just aren't being efficient, on top of it all.
True...but if they get the same amount of tax from my $70 fill up that they used to get from my $30 fill up. Well, that is $40 less dollars I have to spend on other taxable goods. So I would think it hurts down the line.