I definitely don't spend a lot of time listening to political speeches, but since when do people expect speakers to cite sources? Informative academic lectures are clunky because it's all "according to", "Dr. Famous So-and-so says", blah, blah, blah. Academic writing and lecturing is drastically different than political speaking (or motivational speaking).
Political speeches are supposed to be persuasive. Regardless of your views on Obama, you have to acknowledge what an engaging speaker he is. He has an oratory style similar to black southern preachers. One common trait in that tradition is to weave quotes and phrases of popular culture into the speech.
I guess I don't get what the issue is here. This has decades of historical precedent. This is tradition.