Many
British pubs have glasses which hold
exactly a pint, when they're
full to the brim.
Account for head, and spillage 'twixt bar and table, and it soon becomes clear that you don't have the full pint you paid for.
Banks's brewery embarked on a marketing campaign, based around the fact that their glasses are oversized, with a pint mark about 1cm from the rim. The slogan is "full pint guaranteed" (catchy, eh?) -- depending on what you're drinking, sometimes the pump even measures out an exact pint.