Will Siri be an ad revenue game changer?

I'm wondering if Apple's Siri is really about pinching search ad revenue from Microsoft and Google. Is that why they are crapping themselves? This summary seems to point in that direction.

Ask it for advice and it (Apple) gets to filter the results. Just like Google does, but less transparently.

And let's face it - Apple don't build any tool like this unless there is a way of locking in a new revenue stream. Just like how their new Newstand locks in their ability to skim from subscription fees.