This is not about the politics. David Limbaugh has written a column about Rush Limbaugh and it hits all the usual boilerplate junk about the right's view of liberalism, but nowhere in the column does David Limbaugh acknowledge that he's writing about his brother. He's certainly not embarrassed by the affiliation (that's the only reason he's at the level in the con ecosphere he is) and he's firmly on the far right, but he doesn't once make the connection.
It's just kind of weird.
(Link found via Glenn Reynolds, who seems to now be a Rush defender - a far cry from a few years ago when Reynolds made himself out to be some sort of independent libertarian - though some of us knew this a long time ago)