These arguments are, of course, absurdly easy to refute. But that's not the point. I doubt that people like McAuliffe and Lanny Davis actually believe the crap they're dishing out, but they're making these arguments for a reason beyond just firing up Clinton's supporters. They're trying to show just how tough Hillary is.
1. Hillary has gotten more votes and delegates since March 4th.
2. Hillary has gotten more votes in a nomination race than anyone in history. "Hillary Clinton has now received more votes than any candidate ever running for president in a primary."
During the 2000 Florida recount, Republicans, largely led by James Baker, made all sorts of ridiculous arguments to justify two things which were thought to be unjustifiable: that votes in a close election should not be recounted, and, in contradiction of the U.S. Constitution, that a state should not get to decide how its electors are determined. And Democratic opinion-makers would largely sit there with their jaws on the floor and say, "That's a stupid argument. You can't say that." But that didn't stop the Republicans, who figured that if they won, the presidency would provide its own legitimacy, and if they lost, no one would remember or care what they'd said. And they were largely right.
Team Hillary is trying to show that they're just as tough as the Republicans. There's no argument too irresponsible or too stupid to make. Winning is everything. And there's a fair chunk of superdelegates who find this argument compelling, especially if the 2000 election is at the back of their minds.