Fast,
For us up here, this is what I mean by it...................My friends at PF/PH have an agreement that we will be at 250kt by SLP but we try and expedite this as best we can.
We love speaking to you all but its better for planning if we transfer you early and once we have descended you to the agreed level, off you go. By saying speed 250 through 90, we are meeting all the requirements of a silent handover which saves us a phone call.
The other reason maybe that the controller is trying to close a gap but not screw the final approach person. You maybe in the middle of a sequence and to bring you back straight away would mean a reduction in the gap too the one behind. We understand you cannot descend and reduce so this instruction should make it easier.
Hope this explains it. We would love to give you straight in and no delay but there just seem to be so many of you. If you are ever unsure, ask.....or even better, come in for that visit to the centre!!!!!!!! PS If your unhappy visiting in me here in Scotland...........I'll be in Dubai in 2 months!!!!! Ha Ha