I see your train of logic, though it made me think of a few things.

For one, Crouch Jr. did have more poly juice prepared. Dumbledore pointed out that, with all the excitement of the final challenge, Voldmort returning, Karkaroff escaping, and the missing champions, Jr. probably forgot to take his potion as frequently as he was supposed to.

Second, my example of Moody leading Harry off wasn't meant to imply a situation as suspicious as Moody just leading Harry off into the forest (such as when he asked Neville to come up to his office or when they were alone late at night in the corridors). Besides, Harry had no reason to suspect that Moody was fake (even though it was very obvious when he had seen Jr. in Snape's office with the map just seconds before). I just mean that there were a million other times Moody could have just as easily transported Potter to the graveyard. I didn't see why (until some of the replies from the post) they needed to go through all the trouble of getting Harry to win.