I have seen this happen many times. People rely heavily on the remote key fob and don't normally use the key to open the door. What I usually do in this case is spray something like WD40 or another good penetrating oil into the key lock cylinder. Then take the key and work it in and out about 20 times. This will loosen the tumblers up and allow them to start moving again. Once the tumblers are moving you will be able to turn the key and unlock the door.
On some stubborn cases I use a key that is brand new (never been cut). This key blank will allow the tumblers to move fully in the bore and will break them free of the corrosion bond.