The polls can't actually measure support for a public plan...I thought the 30-40 point swing depending on the phrasing of the question makes that pretty clear. The polls indicate low information, not firm attachment to any particular set of plan characteristics. The difference between suggesting a public plan would "compete with private insurers" and give people a plan to choose "if they couldn't afford" one from a private insurer is pretty slim.
it plays easily into the MSM narratives about McCain (i.e. he understands why you hate politics, he does TOO!), but more to the point
as a statement, it's self-deprecating rather than unintentionally self-revealing. The viewer/reader finds himself agreeing with McCain, "Yeah, those folks are out of touch...this McCain guy knows where it's at."