HOWEVER, the seals will age, get dried out and eventually crack. That is what weather seals do and it occurs natually in the course of doing its job to protect the insides. Although it is considerably heavier than most Canikons, I bought the K7 so it could take great pictures in some great places, and not just from inside a car or a building.
I would not worry about them aging too much. I have a 11 year old Kodak DC5000. Its weather sealed (rated IP54 and for 3' drops onto concrete) and as big and heavy as a K10D with a prime on it; an old 2mp digital P/S. The seals which are rubber are still very pliable and soft, not brittle. The camera still holds off water.
Pentax dSLRs use silicone seals in most places where there is movement, buttons, doors, dials. More simple weather-sealing is used on seams as there is no wear and tear on those areas unless you remove them. The service manual tells the tech to check the weather-sealing and replace if it shows any signs of wear from de-assembly/re-assembly. There are a few areas of the body parts (like the seals for the dials) that need special attention by the tech if the camera is taken apart.
In any case silicone will last a long time, and so should the seals between the seams. Now if your serious about life time, perhaps not, how about a long time?
BTW this is IMO, Happy New Years