USE OF AIR SPOILERS
The bus, like many modern airliners is fairly slick,ie reluctant to go down and slow down at the same time. In order to maximise runway utilisation controllers will feed aircraft around base turns prior to the ILS at speeds designed to achieve the correct spacing.They may also reduce ground track to further help. So if you are 220 knots on base and fed in fairly tight or even if you intercept the glide at 180 kts and the headwind is light some speed brake or an early gear selection will be required.
The deployment of speed brakes will as you suggest cause an increase in the red line ( minimum speed you are allowed to fly). This can be countered by flaps