There is of course some overlap – if Obama appeared on Meet the Press he would be promoting his ideas just as much as he did on Leno, but David Gregory would be asking questions more directed at uncovering hidden bits, unintended consequences, and subtle points of Obama's plans. Gregory would be tasked, to some extent, more as a devil's advocate than Leno was required to be.
The line between news and entertainment is constantly getting blurred, and I think that to some extent such a thing is inevitable. Many people will tell you that there's a softening of "hard news" stories. FOX News doesn't find it necessary to remain objective and non-partisan, and increasingly MSNBC doesn't either. But, both those channels tend to remain true to their goal of presenting the news and opinions on the news (in some sort of "entertaining" fashion).
Pushing an entertainment show more towards news makes me somewhat uncomfortable. I think that's because, at least in this case, I'd rather have the guy running the country answer hard questions and defend and fight for his beliefs in the most challenging forum possible. I'm neither saying he's right nor that's he wrong with his economic stimulus plan, I just would rather he was required to actively defend it rather than just have someone lob easy questions at him.
But, you'll find the video below, judge for yourself.