Word is that the finish to CM Punk and Brock Lesnar's SummerSlam match was changed just days before the event. The reason for the change may have to do with the rumored Lesnar vs. Undertaker match at WrestleMania 30.
Lesnar's contract reportedly included three wrestling matches a year, which means he has one match left, which would be at WrestleMania 30. The feeling from WWE officials is that even with the long break that Lesnar would have, they did not want him heading into a match with The Undertaker with a loss at SummerSlam, and overall losing record in WWE.
At this time, Undertaker vs. Lesnar is not confirmed and as always, things can and always do change.