A US pint is 16 fl Oz vs a UK pint which is 20 fl Oz, so add 25% to the US price to do a like-for-like.
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.