It answers the question though if you stop and think about it. If a document opens in a program that can render any plethora of whatever, you don't know what is going to happen when you click that link. With Gemini, you do: a document is going to be fetched that has words in it and those words are going to be displayed on your screen.
Thats not what they are talking about. They explicitely said using existing browsers, not making your useless html4 only browser.