Happens all the time to airfields with a steady mix of fast prop (Saab 2000/Dornier 328 etc) and jets.
In the LTMA we get this too. Probably a difference between the AREA controllers and APPROACH controllers (Two separate "trades" if you like") not knowing each others jobs.
There are a million reasons why an order is decided - sometimes for the wake vortex if you all arrive at the same time, thus saving the total track miles of all involved, sometimes depending on departures. Also depends on levels as well as speeds to 4 or 6 DME. (If you can do 250 kts til 4 then that would help sometimes!!)
All I can say is that as an Approach person, I have NEVER (and no controller I know does) deliberately delayed jets for the fun of it. Everything is done for the good of ALL.
I guess you have never visited EDI tower and seen why this may happen? DO SO fella.