This seems to indicate that a fully-working demo is not what you want to present to YC. Since all you have is ten minutes, I would think you'd want a more focused form of presentation.
Put it this way -- are you a magician? If you present a demo that effectively says "pick a card, any card," you'd better be. If you're demoing Google (the site it is today) for YC, it's probably not the best sell to just let someone type anything they want into it.
When you only have ten minutes, you need to retain as much control as possible over your message. Present the article to sell the magazine.
Showing the sexiest, meatiest part of a working demo is probably a good compromise. Without a demo, you're left describing that same part, which is inferior, right?
Put it this way -- are you a magician? If you present a demo that effectively says "pick a card, any card," you'd better be. If you're demoing Google (the site it is today) for YC, it's probably not the best sell to just let someone type anything they want into it.
When you only have ten minutes, you need to retain as much control as possible over your message. Present the article to sell the magazine.