Baggersup - I think you've misunderstood the OP's query. He's talking about checked luggage (to go in the hold), rather than the temporary carry on restrictions.
Re the original query, I don't think it was ever a regulation. I always got the impression that because it was America, the airlines expected people to take more with them and accounted for it by gracing pax with a larger checked allowance. As jarvy rightly says, BA's regs changed in October; along with the new charges came the 1 bag standard allowance worldwide (except some connecting flights). You can check in up to 10 standard size, standard weight bags - it just starts getting veeeery expensive after bag number 2!
As another poster rightly says - airlines are not charities. And whilst we can all whinge and moan about them stripping down the value of the flight and adding on all these extras, it's hard times. IATA continually report they expect the industry to lose x billion to year end.
Personally, I don't think £32 to take a second bag over 3000 miles to the States is that expensive. Lets see - the Blue Marble mapper says JFK is 3441 miles from LHR on the Great Circle. Thats... a 0.0093p a mile to take your extra shirts and smalls. Absolute bargain if put into perspective...