Why does soda bread call for buttermilk? I've been looking for a soda bread recipe to try and I notice that most of them contain buttermilk.  Buttermilk is not a standard part of my pantry.  Part of the appeal of soda bread is that it's quick to throw together, so having to go shopping for a specific ingredient interferes with the spontaneous aspect.  

I know there are lots of substitutions for buttermilk (using a bit of lemon juice in regular milk is the one I usually use), but I'm wondering what it is about buttermilk specifically that seems to be a standard part of soda bread. Is it just traditional?  Or will it add a particularly noticeable flavour/texture?

Edited to add: I know that its functional purpose is to provide an acid to react with the soda for rising; so is it just that it used to be the most convenient acid?
Buttermilk has a delicious flavor that is not at all approximated by lemon juice. 

It's true that lemon or vinegar with milk will clabber it a little and provide the acid that the recipe needs but the flavor will be distinctly lacking.

Get some buttermilk. It's inexpensive and has a longer shelf life than normal milk. It is also exceptionally easy to make. If you make it a standard part of your pantry you will find yourself enjoying life more (or at least pancakes.)