A very interesting question indeed.
I'm looking for one specific answer :
Is it the responsibility of the ATC to enforce wake turbulence separation ?
If so, I would be very worried because several ATCs cleared me to land or takeoff behind medium jets, well before the required time, while I was flying a 800kg aircraft.
Or is it the responsibility of the captain to ensure that the separation is satisfactory ?
If he deems it safe, can he reduce the separation ? (e.g, strong crosswind)