tl;dr Obama did lie. But every one else lies in the same way for the same reason so he probably didn't think much of it, and neither did anyone else.
Politicians openly game the system. They poll, then they change the message based on the poll, then they win. Then they do whatever they want since the platform on which they ran was a total fiction.
In truth, the only platform that really matters is the party platform. A career politician ignores that at his great peril, as they risk losing the support of an incredibly efficient, effective political machine.
And this is nothing new. The new thing is that, in an effort to feel sophisticated, more mainstream Americans are pushing aside the initial feelings of disgust. They tell themselves the story I've told above, and they tell themselves that that feeling of disgust is naive. It would be like being disgusted by gravity - totally pointless. The same thing occurs in the private sector, when bank leaders commit fraud and walk away. The fraud is explained away "well, he was just acting in his own interest" and the walking away is explained away "well, powerful people look out for each other."
The simple truth is that we need to stop pushing aside that feeling of disgust. It's there for a reason. We have an in-built sense of fairness that our government, and our business leaders, ignore at their great peril.