The fight wasn't over in the first round, it went the full five rounds because JDS did'nt give up like many other fighters likely would have after taking a beating like that one. And Cain wasn't sloppy, he smothered JDS the entire fight but I guess JDS nuthuggers have to have an excuse to make themselves feel better.
I think that fight went five rounds because Cain made sure he didn't fall into a cheap submission on the ground. Wrestlers can be very successful against BJJ if they avoid positions where they can get locked.
The beauty of Cain's performance is that he went for basically everything except leglocks. Armbars, leg kicks headkicks, even a (failed) hip toss, and of course standing toe-to-toe with a guy who knocked him cold.