I don't think the buttermilk ice cream is made from teh same buttermilk that the OP is referring to. The milk leftover from the churning of butter is a kind of tangy skim milk and it can't be used to make ice cream because all of the fat has been removed to make the butter.

The buttermilk you buy in the store is basically fermented milk. It has a totally different flavor and texture. It is also delicious and you should totally make fried chickenburgers with it. You should also make biscuits, pancakes, cornbread, etc with it (assuming you eat those things) because buttermilk has an amazing flavor that's really unlike anything else.