^^^^^^^^^^
Funny aaronji, I read Jon's comment and thought, yes he is correct in most USA cities about convenience stores or pharmacies. Which due to rampant unthinking real estate expansion it is a fact that many communities in the USA have two pharmacies at almost every major intersection!
In the EU, where train travel is more common and I can't speak to the amount of pharmacies on each corner, but am willing to bet there aren't as many, I can see where the 9Volt would be more ideal.
I can buy A23's or 9V's equally as easy here in the great state of NY.