dear pulsartek
spoilers can actually be used in many ways.
spoilers can be used to augment roll control, in which case spoilers will come up on one wing and not on the other
spoilers can be used as speedbrakes, in which case they will come up on both wings at the same time.
spoilers can be used to destroy lift upon landing to ensure all the weight of the plane is on the wheels which helps stop the plane using wheel brakes.
and the funny thing is the spoilers can, but not always be, the same piece of the wing...just used in a different way.
Some speedbrakes on planes are different, the BAE146 has a funny little speedbrake on the tail of the plane. Speedbrakes on some fighter planes are really funny looking, and usually on the fuselage.
So, yes it was probably normal that you saw these spoilers deployed to aid in descent. And yes, if you kept the spoilers out you would probably stall at a higher than normal airspeed or you would reach the stalling speed much faster by having the spoilers out.
And there are some planes you are not to extend spoilers when the flaps are extended
And there are other planes that you CAN extend spoilers when the flaps are extended.
AND if you want to ask the pilots next time, be sure to do so...you can easily sound like you know what you are talking about by saying: DID ATC KEEP YOU TOO HIGH? I saw the spoilers out.
So spoilers can be used, in different ways at different deflections for different reasons.