The last time the Super Bowl aired on CBS there was also a spot with Letterman, it as well featured Oprah, and this year's promo was certainly building off any audience memory of that one as well as the famous "Uma, Oprah! Oprah, Uma!" introduction. While that certainly played into the joke itself, from an industry standpoint, the presence of Leno is what really made the entire experience somewhat odd.
For years, when Leno hosted The Tonight Show, something he'll be doing again in a few weeks, he routinely beat Letterman in the ratings. In fact, as has so frequently been reported with NBC's recent late night woes, it was only after Conan took over the host duties at The Tonight Show that Late Show began winning the ratings war on a regular basis. Thus, in a very real world sense, Letterman would most certainly be displeased with Leno's returning to the late night party.
Why then did Letterman do the ad? I'd like to think that the answer is because it was funny – making the joke was funny and Letterman is nothing if not a funny man. Additionally, Letterman, as we saw with his personal scandal last year, is able talk openly about, and therefore get out in front of, issues – be they personal or professional – that he may be facing. Leno's return to the late night scene is, potentially, definitely an issue for Letterman. Leno was the ratings king before his departure to primetime, and the current question among pundits and industry execs is whether or not he'll be able to regain that crown.
Why then did Leno do the ad? Through the current late night issues Leno has certainly been made the bad guy. When he's talked about it, Leno has painted a picture that has him as something of an innocent with NBC's plans, but that hasn't stopped others from knocking the once and future Tonight Show host. Perhaps Leno did the promo spot for Letterman in order to finally show that he has a sense of humor about himself and the situation. And, whether or not he was an active participant in a fight with Conan or not, Leno certainly came out as the victor in the battle – Leno remaining on the air at NBC despite the low ratings for his primetime show and Conan leaving the network. Leno doing the promo as a way to help rehab his image is incredibly smart, and NBC's allowing him to do it is equally bright.
Yes, the entire thing was apparently Letterman's idea and only required Leno, NBC, and Oprah to sign on, but NBC and Leno could easily have seen the spot only as one for Letterman and shot the whole thing down without anyone being the wiser. They didn't do that. Instead, Leno and NBC agreed to do it and what we, the audience got, was a spot for Late Show that ought to help rehab Leno's, NBC's, and The Tonight Show's images as well.
Plus, it was funny.