Actually, Leno has nothing to do with it. Executives at NBC choose appropriate time slots for the shows based on ratings/number of viewers. I doubt Leno has any say in that process. And it was, in fact, Conan's show that flopped, so NBC chose to put Leno back in that time slot.
Both their shows' ratings were "low".. but Jay's show was new.. and so there wasnt something to compare to.
I also felt (as mentioned in the thread above) that Conan held back.. Conan has his following, but the Tonight show has its own. So the followers of the Tonight show were gonna make comparisons between the 2.. so Conan was trying to take it easy til people got familiar with him and his style of humor.
I believe that NBC was behind the time slot change, but Jay could have said something so that Conan could run his show as well as Jimmy Fallon. Jay has been on NBC for a long time, so he has some influence.
This is what I've come to understand... regardless, Conan is gonna have opportunities for his own show. But the fact he had the "Tonight show" name made it more traditional.
I do like some of Leno's jokes as alot of the late night hosts.. But Jimmy Kimmel and Conan are the guys I like to watch and I think their formats are better.