What I don't understand is, you aren't allowed to take anything flammable (including alcohol) on the plane, but you can buy as much alcohol as you like on board.
I think you'll find they mean things with high concentrations of alcohol which are easily flammable. I personally havent managed to set light to lager but there's always a first!
I personally think they should ban drinking on planes altogether. I find it funny that you can't drink on the London Underground but you can drink on a sealed aircraft going 100s of MPH.