I would agree that it really varies by saddle. I was riding a Terry Fly on my last road bike. When I got a second bike, I put the old Fly on the second bike and bought a new one (same saddle) for the road bike. I was amazed at how different the new saddle felt. It was identical to the old one, but it felt WAY different (harder at first, but more supportive and more comfortable over long rides). The old one was 2 years old and had about 4,000 miles on it. I think it was already breaking down significantly and I didn't know it until I'd ridden a new one! I kept riding the older one until it got to the point where it would HURT on rides over 65 miles long. At that point, I had to replace it.

This is why I wish I could get a Terry Fly with slightly less padding. I have heard that saddles that are less padded tend to hold up better over time (hence the Brooks saddles left from the stone ages that are still in use! ).