Even in English it isn't consistent, ask a Canadian how much they drank and they might say "oh, I had a few beer".

Interesting one. In my ear "Biere" would only sound right when referring to distinct beer types. I think this is more a case where spoken German would prefer "3 bier bitte" but technically it should be "3 Biere". Reminds me of the old joke where you hold up two fingers and say "4 Bier fuer die Maenner vom Saegewerk".