Well, some cars do have the sensors. This I know for a fact. My 2003 4,6is has one sensor inside each valve.
I found this out when I changed my original 87 20'' wheels with aftermarket 214's. I was under the impression that only the wheel speed sensors were used for the ''RDC'' tire pressure sensors.
After changing wheels I got the ''Tire press. control inactive''.
Needless to say I did all the ''reset'' acc. to the owners manual.
Now I have 4 pressure sensors laying on my workbench in my garage ready to be fitted in my 214 wheels.
Go Figure.......