I guess I'm the only one who actually thinks JDS showed a very decent ground game. BJJ is not only about the guard. JDS prevented most of the guard passes, he turtled well, always worked for the same side underhook from halfguard to stand up.
He simply decided that he would be better off using his BJJ to stand up rather than remain on his back and work for submissions.
Also you can't forget that Cain is very legit on the ground aswell. Besides his wrestling credentials he also trained with Dave Camerillo for several years and is a brown belt under him. He has lethal ground and pound and superb top control. Just look at what he did to Big Foot, who is a very well respected Black Belt in his own.
One last point you have to consider is that nowadays you rarely see successfull guard work in heavyweight MMA. Mir had some success, but the submissions he got from his back weren't against the best grapplers out there. Even Brock shut him down in there second fight quite easily. Now the only guy in the heavyweight division who nowadays possesses a guard that is a real threat is Fabricio Werdum who simply is one of the best grapplers in sports JJ aswell.
In my opinion JDS had the right gameplan with getting up from his back and using his BJJ the way he did. He did not lose the fight because of his groundgame but rather because of Cain's relentless pressure and TD threat which ultimately lead to JDS being to concerned with TD defense and leaving himself open for jabs and straights by Cain.