xxx,
The cabin pressure system is designed to maintain a pressure differential (generally about 9psi), rather than a cabin altitude. ie if the aircraft climbs to a cruising altitude of lets say FL200 then the cabin might only climb to 2500', but if the aircraft climbs to a cruising altitude of FL410 then the cabin altitude might be up around 8500'.
In addition, the human ear can only comfortably handle about 500'/minute rate of decent, so the system is programmed to descend at a rate approximating this. That is to say that when the aircraft starts descent the cabin pressure will also start descent so that both reach the landing altitude at the same time, but the cabin has significantly less rate of descent, giving a more comfortable pressure change for passengers.
Cheers!