That's the impression that the press would like you to have. This is about foreign intelligence. The law that allows the president to electronically eavesdrop via the Department of Defense (NSA) is the Foreign Intelligence Security Act. The law in question has been tested in court and the President's powers in this area affirmed.
We have been monitoring foreign electonic communications since before World War II. Ever heard of Enigma, Ultra? What has changed is the type of war. Rather than intercontinental missiles, we have sleeper cells.
If we discover electronic communication coming from an Al-queda leader to someone in the US, do you want us to ignore that? Spend 72 hours getting a warrant rather than perhaps learn what their imminent plans are?
The problem with this is that it says that the President, as CIC in time of war, is not subject to any statute. While I don't have a lot of problems with Bush's actions to date, this is not a power I want future, unknown, Presidents to have.
FISA lets us listen immediately; the 72 hours is the time we have to get the warrant after we start listening.