I think also it's 'fridge dependent. We normally buy skimmed milk, which last ages, much longer than the 3-4 days it takes us to go through 4 pints. My wife has been drinking full milk as well recently, and an opened 4 pint bottle is lasting nearly 2 weeks with no ill effects.
My view is that the supply chain for supermarket milk is much, much better controlled in terms of termperature than that for bottled milk via dairies, and throughput is also much higher.
Plus all supermarkets still sell 2 pint containers, which are hardly huge.