Same with mattresses. I know the one i replaced last year, i believe when I bought it, the conventional wisdom was it should last 10 years. I pushed mine, and it was 19 years old when I got rid of it.
Definitely notice the difference in my new one, but now, advice is they last maybe 7 or so years. Of course different factors etc. come into play, but even so, I'm not too thrilled at having to shell out all that money more often!