If its against the law then how does my car pass its MOT?

I dont have a friendly MOT tester and the last two MOT's have been done at stations 30 miles apart. As for the smoke results they have been well within the limits and at no point was the car flashed back to standard
However what I do find strange is the smoke test is done whilst the car is sat still. Revving the engine whilst stationary does not put anywhere near the same load on the engine as whilst in motion so to me its a bit pointless

With regards to TPMS how can you test something if its not fitted?
For DPF's to become part of the MOT EVERY diesel car has to be fitted with one from manufacture. Yet not all all or where. My father in law has a 2007 Fiat Bravo with a 1.9cdti engine but not DPF. Yet the same model built in the same 6 months with the same engine has a DPF fitted. Should the father in laws car fail the MOT because there is no DPF??