Oh, yeah, UHT can last for ages on the shelf. But I read it as referring to ordinary milk, in the refrigerator. "When I lived in the UK a pint of milk would last a week or so at most" sounds about right for that.
I personally think there's a big difference in taste, and I don't use UHT unless I really need to, but I'm sure that's partly just snobbery. You're right that it's perfectly OK for most purposes.
It's kinda wild it has as small of an impact on taste as it does. There's absolutely a difference, but it's surprisingly decent.