After reading this and all of eli's posts below, I believe this is referring to the way Instawallet works, and not the "green address" system. But to both of you: WTF, be more specific. It sounds precisely like you're referring to the use of a single bitcoin address as being some horribly insecure concept, and somehow relating to a URL in a way that makes no sense.

Instawallet (appears like it) works by giving you a bitcoin address, and a unique URL which gives you access to send money from that address. From that perspective, I agree: horrible, horrible idea for safety purposes. Bookmarks rarely (ever?) have secure storage.