Some place in the Owners Manual it talks about why if you change to the spare tire the low pressure light comes on. This is because the spare does not have the sensor. So it's there, just not as clear as the big bold letters on the cover of the Hitchhikers Guide to the Galaxy.

Hope this isn't true. Just rotated my tires and included the full-size spare, thinking it was smart and would stretch tire life. It doesn't make much sense to include a full-sized aluminum wheeled spare, and not include the sensor!