This line, packed a decent way down into the article in the Washington Post, jumped out at me as the most significant ...

Government access to call records is related to the previously disclosed eavesdropping program, sources said, because it helps the NSA choose its targets for listening.

This seems key.

This isn't yet another program with civil liberties concerns hanging around it. It's an integral part of one program. This is the initial cull, from which targets of interest -- that wouldn't be able to meet 'probable cause' standards -- are chosen for actual monitoring.