I can not comment on the reduction in wake turbulence separation standards to (not) answer the original question.
In Aus we apply airborne to airborne.
My understanding is that wake turbulence corresponds with lift.
The moment an aircraft becomes airborne...ie lift is greater than gravity...then wake, or significant interference of streamline airflow occurs...resulting in turbulence!
It is interesting to note, on departure, firing a (M) behind a (H), or a (L) behind a (M), 5 miles or 2 minutes is required...AND with a slower following aircraft, it is more efficient to use a distance standard, or approximateley 1.5 minutes!
I would also like to point out the inequities in departure vs arrival wake turbulence standards...but that is for another day.
My 2 cents worth...please feel free to correct.