Pakistani rulers play on different tables, not unlike the Saudis (and the US). They used Islamic extremists in Kashmir and in Afghanistan to pursue their own goals, so they wouldn't just drop them like a hat the day the US came knocking. There is ample literature on the mutual distrust between US and Pakistani security services during the "war on terror".

In many ways, Pakistan is like Saudi Arabia or Turkey: countries the US cannot afford not to be allies, but with very different strategic interests, often conflicting with US ones. I don't find at all strange that they might have harbored Osama all along, just as another bit of leverage in the eternal game of foreign policy.

There has been a good amount of U.S. aid money going to Pakistan since the war on terror. Pakistan would have the incentive to prolong the war on terror, may have reasoned that a living Bin Laden was a cash cow.

I don't think you quite understanding how institutionalized statecraft works. Think of it in this way "Pakistan knew where OBL was and told the US - for what gain?"

In case they needed a trump card to make nice?

an ace in the hole, as well as a lot of saudi money (as reported by hersh)

The same possible gain that motivates people to blow themselves up and crash planes into buildings and burn churches and synagogues.

That is, no possible gain that a rational person would understand. But Islam is not a rational memeplex.