The liquid restrictions (bottle size, ziptop bag) are rules of the federal transprotation security administration (TSA) and not the airlines. The airlines' only concern is whether the stuff you get past security will fit under the seats or in their overhead bins.

The official size for liquids is actually 100ml or about 3.38 liquid ounces.

They post 3oz as a round number. I travel often with a 3.25oz deoderant and other metric sized bottles with no problems.

The 100ml makes the USA compatible with the restrictions now in place around Europe and the rest of the World