This is because raw milk has not been pasteurized (heated up) and therefore retains all of the enzymes that natural to milk, including lactase, the enzyme that helps us digest milk.
We are raw milk converts now. Especially when it's from such a reputable source, a farm that has never had any issues with contamination or food poisoning, we are happy!
We buy from http://www.organicpastures.com/ though not online. They have a "hub" (a truck, essentially) in Glendale where we buy their stuff for almost half the price they used to sell it at Whole Foods Market. A family at our Bible Study also buys from them and they've been drinking their raw milk for years.
I am a total "natural parenting" mom, so guess what Noelle is going to be drinking once she can start dairy?