That's the problem: there's no way for that to happen. Imagine Amazon started offering 5% off with Bitcoin. Visa tells them to stop it or they'll lose their account. What do you think comes next?
The big retailers have too much to lose if they can't process credit cards. Small retailers are unknowns and thus potential scammers.
Stop living in the fantasy of what the world would look like if everyone used Bitcoin and start thinking through how one could actually get there. It's far from easy and probably impossible without some fundamental changes to Bitcoin itself.
Imagine if Borders bookstore told Amazon that they cannot compete with brick and mortar stores because customers can't send cash through the mail? Would it now be Amazon that is bankrupt instead of Borders? Whodathunk it? Stop living in fantasyland that never sees technology advance progress. Visa does not run on magic. Once venture capitalists see the potential of investing in decentralized payment processing, they will flock to places like MT Gox, Trade Hill, Intersango, etc.