Because you get yelled at for doing a blink tag, but it's fine to do a moz-blink tag.
The problem is when browser #2 wants to implement blink. They shouldn't use your prefix, so they now have webkit-blink. And the HTML writer now needs to sniff the browser.
or whatever. (In practice everyone who provides these properties does so in a very similar manner, so it's easier than the above pseudosnippet suggests.)
The problem is when browser #2 wants to implement blink. They shouldn't use your prefix, so they now have webkit-blink. And the HTML writer now needs to sniff the browser.
Progress?