Ultramercial

I don't understand how Ultramercial works. I go to the Economist website, and get free access to the content in return for "watching" a commercial from Deutsche Bank. You can't close the ad, or you don't get the content. You can't skip the ad, or you don't get the content. But you can just click on a different tab in your browser, let the ad run unseen while you carry on with email, and go back to the content once the interruption is done. That's not a complicated work-around for people very used to skipping channels when the ads come on their televisions. Now that IE7 has tabs just like Firefox, isn't this just another interruptive format that's only causing an interruption to the relative technology have-nots?