I have heard that its all in the water, but a friend who spent a summer in Italy somewhere with a master baker laughs at me. He said its due to the different stains of wild yeast that are everywhere. You can grow/start your own sourdough anywhere but some wild yeasts are just not palettable. When you start a culture unless a seasoned veteran you'll actually be growing a hybrid thru no fault of your own involving you local wild yeasts also. You can also culture your own starter of that local wild yeast.
I never messed with sourdough, but I believe Disco does, and does a bunch.
BTW, I recommend a site called the "Fresh Loaf" They are to bread what SMF is to smoked meats. Its funny, I've been there for years now, and everytime I ask someone about there baking info, seems they always refered me there.LOL