edit: Wouldn't you agree that "Digg's HTML" provides exactly as much information as "Digg's HTML markup"? If so then "markup" is clearly redundant. You're really missing the point by saying that not all markup is HTML. All HTML is markup, it's the HyperText Markup Language. Damn.
edit-ps: It's really annoying that I only see my own message when editing, I should see at least the immediate parent also.
edit2: "HTML" does add information to "markup", but markup doesn't add information to "HTML". "HTML" is a "strict subset" of "markup".