If you go to
http://store.apple.com and click on "Displays" in the nav bar on the left, you'll see that Apple sells several CRT monitors made by 3rd parties. Of course, you can always buy one cheaper just about anywhere else. And the whole point of a headless Mac is that Apple isn't "forcing" anyone to buy any particular monitor.
Also, one of the rumor sites said "The unit will easily plug into any display or
television", emphasis mine. Could it be Apple's positioning this as a media center PC?