Unfortunatley we are seeing prices like this in the US as well. I live in Denver, CO and a pint here typically runs between $5-$10 depending on the place.
A fluid ounce is based on avoirdupois, which isn't "imperial", so it didn't have to be abandoned. I think pints, quarts and gallons, all being based on the pint, are the only measures that differ significantly between the US and the UK.