Does your car actually display the tyres pressures on a screen every time you start up, or just give an "ok" signal.
If the actual pressure isn't displayed you will find that there is quite a large tolerance for the pressures before a fault is indicated. The tolerances can be several psi , to allow for when you increase tyre pressures when the car is fully loaded,motorway speeds etc. Even acual driving, when the tyres warm up can make 3 or 4 psi difference, as can the extreme cold weather in the winter.
On our Laguna I find that our "actual pressure" display is approx 2psi lower than any readings I take manually.
So a display on the dash of 32psi gives a reading of 34psi on my manual tyre pressure gauge.
As you say,you cannot beat actually checking these things yourself though, I do every so often, but I find the "actual pressure" display in the Laguna to be very reliable.
As with everything, they are only a guide, as is the
level gauge,the outside temp display & to a certain extent your fuel gauge. Never rely on them totally! Human intervention is nearly always better than machine intervention.