Visa may not comprise such a large share of CC transactions in a couple of years. One reason they control so much is that they didn't allow banks that issued their cards to issue Amex and Discover. That's over now.
http://news.yahoo.com/news?tmpl=stor...n_express_mbna
It would be really interesting if banks started sending Discover cards to all their customers who already have Visa...Power Move?? If you were the CEO of Discover how much would you pay banks to do this?