I'm not a fan of instant title rematches in most cases with a few exceptions like Silva and a few others. The reason is if you do too much too soon then where does it leave you?
I think JDS and Cain fought too much in a short time span. It kind of ruined anticipation for another matchup as they drained the well dry very quickly. Now JDS, who I think is clearly the 2nd best HW after Cain, has been shown to be dominated by him two fights in a row. However, after the prolonged beatings Cain put on him, he has to sit back and put some impressive wins together for many people to start to believe that the next fight would be a little more competitive than the last two were.
I'd rather see a guy fight two or three other fights, preferably in a short time span, get the wins and then get a rematch for the title. If the person who beat them loses the belt before then, then that could be one of the fights they have before they fight for the title again.
In short, too much too soon between the same two fighters could dampen the excitement for any future fight between those guys. If they are both good enough, they'll meet again anyway.