I have yet to see a clip from Conan's tonight show that makes me shake my head in disbelief at how awful it is. My neck hurt a lot while Leno was the host.
I'm feeling old that my generation is now the generation that watches the Tonight Show in numbers enough to cause that audience roar. But I don't think Conan is one of them, he mentioned the "Super Mario brothers People." He did not say Nintendo.
The animation appeared to have a combination of Super Mario World and the Super Mario All-Stars remake of Super Mario Bros., although the music was obviously from the NES version.
#1 He didn't make the reference. The internet made the reference, which he then indulged. He could have taken offense, or ignored it, but he made it into a gag.
#2 Altering that background would probably take a decent amount of man hours to create, so there was nothing lazy happening there.