David Kravets quotes a Googler:

“Google requires an ECPA search warrant for contents of Gmail and other services based on the Fourth Amendment to the Constitution, which prevents unreasonable search and seizure,” Chris Gaither, a Google spokesman, said.

The Electronic Communications Privacy Act isn’t always as demanding as Google, and their assertion that the policy is based on Constitutional requirements implies that the ECPA does not comport with the same requirements. That’s a bold legal position to take, but as Mr. Kravets explains at Wired, Google isn’t necessarily alone.