Yes, Al Qaeda has a web glossy (they used to have an even more sophisticated online media operation but we have drones). And yes, it matters. Inspire is where the Boston Marathon bombers are thought to have gotten both their specific motivation and their bomb-making instructions. When it publishes a call for terrorism against American airports, our intelligence community pays attention. So does Congress.
As for what this will do on the ground: do you remember these guys, the TSA VIPR teams that handle security outside of airports? The ones that have been particularly focused on trains and buses? A terrorist organization responsible for the murder of thousands of Americans has just called for attacks against a rail that connects airport terminals to San Francisco's rapid transit system. We're not saying that you're going to see TSA guards meddling around with airport rail security, but we're also not saying you won't. There's going to be some kind of response to this.
Here's a local news report that does an OK job giving an overview:
[Photo: CBS San Francisco]