Older ones yes (Up to a point) specifically the old analogue ones, but then start to go downhill with age. (Capacitors are the biggest culprit)

Most modern keyboards are also a yes, as most manufactures bring out software updates that improve the sound and features of the models during the production run, but apart from that, no.

Players get used to a particular type of sound (Even though it may not be the best out there) and this is the reason they hold on to older boards. (There is always the nostalgia element as well)

Bill