I don't remember Obama mentioning Limbaugh more than a time or two during the campaign. And there's no mention of Fat Boy in the above quote.
Let's face it, Rush would like nothing better than an ongoing feud with Obama. He has everything to gain from it (ratings, money, prestige).
Obama has nothing to gain from engaging Limbaugh.....nothing.
The only feud is in Limbaugh's Oxycontin-flavored dreams.