It's not fair to compare a film camera to digital, where the technology has been improving rapidly. However, I think we may be near a long-term plateau in sensor performance, so I tend to agree with you on a longer upgrade cycle than we've had over the past 10 years.Guys, guys, guys...
The Nikon F3 had a production run of 21 years (1980 - 2002). Did it made bad pictures after all that time?
I believe a production run of 2 to 4 years is to short. Look at the prices of new cameras - most of it is developping costs.