Most likely, I've had people tell me the central heating must be replaced every 15 years even if it's working, probably on the same misunderstanding.
Surely if it still goes off on your regular smoke tests (aka burning the lunch in my case), then it's working reliably -- stick with it. And don't tell me about bathtub curves -- there's a steep end at the beginning of the life of a new one as well as on the end of the life of the oldie. You should have more than one anyway which will cover one falling over at the shock of actually going off for real.
Chris