I think one of the reasons (some) milk is still sold in pints or multiples is because the dairy industry put up strong objections when metrication was proposed. The cost of replacing pint bottles (unique to the dairy industry) was a big factor, plus the 'romantic' attraction to the daily delivery which I think was pretty unique.
Same with beer. They're were lots of suggestions that 500ml winking cost the same as 1 pint (568ml) because of rip off pubs plus, the idea that it would show Europe to interfere with the in stupor the British pub. Funny thing is, we dont have a problem drinking half litre draft beer on holiday in Europe, or a 33cl bottle, or, in some parts of the word 25cl bottles. We seem quite capable of getting in down our throats without choking. The fact that it isn't a pint, or a half doesn't seem to be a problem. And spirit measures are metric as well for a long time, but before metrication, spirit measures in Scotland were bigger than in England and Wales. That never caused a problem either.
A lot of these things are just hysteria stirred up by the media as if its a threat to us.. As I said, we go abroad and drink different measures of beer, and I funny think any of us feel or eat of life is threatened in any way. Life's funny like that.