Simply filing a flight plan does not constitute a request for PPR; if you don't believe me, try filing a flight plan into Farnborough without PPR!
My comment was only related to Biggin, like the OP's post, not the world as a whole.
From their website:
The booking system is for every aircraft movement unless there is a filed flight plan.
No-one is suggesting a flight plan typically negates the need for PPR elsewhere. Only at Biggin.