I find that utterly amazing. Four years ago, "Obama-mania" was at it's zenith, yet we somehow had 17 million MORE people watching the first debate this year! What does that tell you about GOP enthusiasm!
The first debate in 2008 (also moderated by Jim Lehrer) was a trainwreck for the GOP. If you remember, McCain tried to bail on the debate, claiming that he had to be in Washington to deal with the financial crisis (he had actually suspended his campaign!) but reluctantly showed up once it became clear that Obama was going to be there with or without him.
The debate itself was an unmemorable snoozefest with no clear winner though of course the adoring media proclaimed Obama as the winner while McCain grinned and agreed that Obama was a nice guy and that the American people need not fear him being the president.
I guess Obama was also expecting Mitt Romney to submissively roll over and lick his shoes like McCain did. Well Obama was wrong and 70 million Americans got to see him finally put in his place.