Obama and the Public Option

Today's Glenn Greenwald post links to Ezra Klein's post about the question of whether Barack Obama campaigned on the public option. It's rather a question of semantics. Perhaps the public option was not a major theme of his campaign, but it or what was called a public program was certainly in his campaign.What's the difference?

As of today, what Organizing for America has for the Obama Plan includes a public option.

This is in regards to Obama's recent statement: "I didn't campaign on the public option."