I learned about this in a food safety course, but now I can't remember exactly what they said... Certain brands of dairy have a much longer shelf life than others. I think it had to do with the way they process and pasteurize it versus other methods. It can also have to do with the way it's packaged, maybe
Might have to do with the higher butter fat content. buttermilk and cream have a longer shelf life as well, so that makes sense.
I wish I had the problem of milk hanging around long enough to worry about it expiring. We go through 6-8 gallons a week (2 boys and DH LOVE milk...guess I should be glad), but even with a refrigerator in the garage, it seems I am always running to the store for more milk.