According to Jeff, in a radio interview linked off of wilcoworld.net, it's intentional. Nels tried a number of things there, but the band loves George Harrison, and whenever Nels played that, everyone else in the band smiled so they stuck with it. Similarly, he tried a number of things less narcississtic than "Wilco love you baby," like "Let go, love you baby," but "Wilco's" the one that made everyone smile so they went with it.