I don't think that most enthisiasts, semi-pros, or pros are going to sit on a camera body for ten years. I think your average consumer tends to churn through cameras at a pretty fast rate as well, although there are certainly some who stick with what they've got as long as they can to get the most for their money.
The vast majority of dSLR purchasers never buy another one. Only pros and genuine enthusiasts do. Of all the people I know that have dSLRs, almost all of them still use the first one they ever bought. I'll provide a list of people I know, aside from me - 10D, D70, 5DII, Rebel XT, 300D, T2i, T4i. In fact, of everyone I know, only one person aside from me has ever "upgraded" and that was to move from Canon (40D) to Nikon (D200 - still using that one). And my upgrade was from 10D to 5D when the 5D first came out.
This next path (looking like 20D+5D to 7D2+6D) will be my first body upgrade since 2005. I've cycled through a great many lens changes since my first DSLR purchase (17-40L, 28-135IS, 75-300IS, 50/1.8, 50/1.4, 35/2, 35/1.4L, Sigma 20/1.8, Sigma 15mm fisheye, 100/2, 85/1.8, 24-105L, 70-200/2.8L IS, 70-200/2.8L IS II, Tamron 1.4x, Tamron 2x, Kenko Pro 1.4x, Canon 1.4x II Canon 2x III, Meade ETX-125PE, Celestron Edge HD 11).