There were a couple of guys who did not pan out, but I really think the reason for this is to keep everything focused on Stars Hollow.
The time that Rory spent at Yale early in the season did not work that well—they pretty much need to bring her back to keep the dynamic of the show—mostly the interaction with her mother. What seems to be working best at Yale right now is the deal with Paris and the professor. And that may well just be the parallel plot to Rory making a decision about her married man.
If she were involved with a guy from Yale, that would just make it harder for the continual returns to home.
I think Jess's return, and Dean's return is to wrap all of that up more satisfactorily than they had so that Rory can move on to the next love interest. Jess was left open last season because they would have wanted to do crossovers with his show which never flew.
I did read that:
Rory's new love interest has been found, Amy Sherman-Palladino had trouble finding an actor she liked for the role, and will be introduced on the season finale.
I thought this episode was great, vintage "Gilmore girls." It's the end of the fourth season, so I think it's time to lay the ground work for Luke and Lorelai, which will take all of next season to go anywhere, but should be a fun ride.