Normally, it is a (usually) unwritten rule that you walk on the right side. (at least, that's how it is here.) I, myself, usually walk on the right side, just since its easier (since most other people walk on the right too.) I have no idea about the other countries...I'll ask my best friend. (who just happens to be Scottish)
Maybe it has something to do with dextrosity (is that a word?). I'm definitely going to look this up now. I'll let y'all know when I figure it out!
I honestly don't think it has to do with the side of the road you drive on...I don't drive but I do walk on the right...