What in the interface tells you that navigating away from the page will not submit the data?

Perhaps instead of reset a "do not submit" button is required. But then if I changed my mind about what I'm writing but still want to send a message things get a little lame.

How can you tell for example that going back doesn't instead save the comment as a draft (like the SMS interface on my [pretty old] Sony Ericcson phone).

I disagree with the article, I think there is a place for a reset/clear function.