Easto said:
I think they waited until round 6, so Lewis could keep his title. If they stopped the fight earlier, they would have had to go to the score cards and Klitschko would have won.
I don't mean to defend Lewis but this is incorrect. The cut was caused by a legal punch so Lewis would win by TKO whenever the fight was stopped.
The scorecards are used in the case of an unintentional headbutt, and then only once the fight has passed 5 rounds. Before 5 rounds are complete the bout would be a technical draw. But in this case the cut was from a punch, so Lewis would have won by a TKO even if the cut had been stopped right away in the 3rd.