It is mostly the pace of technology that has driven the massive devaluation of newer cameras. It is no different than PC's in the 80's and 90's. The technology was advancing so fast that your PC didn't lose value because you were using it, it lost value because in 2 or 3 years it was seriously outdated technology.

Besides, have you looked at the specs of a 2005 Pro camera?

Some specs for a very expensive PRO DSLR available in 2004, and throughout 2005:
8mp, ISO 100-1600, APS-H sensor (1.3 crop factor), 2" LCD (2.5" LCD version in late 2005).

Specs for a relatively inexpensive consumer DSLR from the same company available in 2009:
15mp, ISO 100-3200, APS-C sensor (1.6 crop factor), 3" LCD.

Admittedly the Pro camera has some other advantages, like a larger and 100% viewfinder, faster shutter, better build. But the point remains, you could basically get a similar or better camera 5 years later at the consumer level, which greatly devalues the pro model.

Also manufacturers quit servicing older cameras eventually and that can greatly decrease their value, since they become a brick if they break.

I think it might be hard to tell the 2004 from the ~2007, or the ~2010 from the 2012. But the 2004 would be pretty obvious relative to the 2012, and the ~2007 could probably be discerned as well. Especially with the 16x20 print since you really want at least 10mp for that, preferably 12. And that all assumes ISO 100. Because as ISO rises the older cameras will become more and more obvious. The colors fade, they lose contrast, and they just generally don't look nearly as good. Even my 5d3 blows my old 5d2 away at just ISO 3200, making telling apart the photos from each pretty darn easy.

I find spending too much time on forums triggers my GAS reflex. I do enjoy my new toys, but at the end of the day, I tend to wait out at least one full product cycle before an upgrade, and spend the change on glass.

I bought into M43 when the E-M5 came out because it was the first camera in the lineup that ticked all of my boxes; compact, good EVF, and above all great IQ competitive with high end crop factor cams.

I resisted the urge to upgrade the 5DII to a mark III because, simply put, the pure image quality improvements are minimal at best, and I very rarely shoot subjects where the mark II's autofocus system made a difference. The 'sweet spot' seems to be upgrading bodies every other (sensor) generation.

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EOS: 5DII, 30DIR, 24-105L, 35L, 135L, 15/2.8 FE, Σ 50/1.4, Σ 105/2.8 macro
Mu43: GF2, E-M5, P14/2.5, P20/1.7, O45/1.8, P7-14, O12-50, P12-35, P100-300
Legacy: Contax Zeiss 50/1.4, 35/2.8, Leica R 50/2.0, 28/2.8, Pentax 50/1.7

I don't think there's anything odd about it at all. I re-entered the photographic world (at a level beyond point and shoots for family snaps, anyway) just over two years ago. I got an Olympus EP2 - I loved it, but after a few months of shooting with it and getting my chops back a little bit, I sort of developed a mental wish list of the things I'd like it to do that it didn't and of things it did that I'd like it to do a lot better. That didn't mean I didn't take some photographs with it that I'm very happy with indeed. But I also missed a lot of shots where the equipment actually WAS the limiting factor. Almost exactly two years later EVERY item on my wish list came together in the EM5, plus some things I'd have never even hoped for but that prove very useful (the IBIS in this camera never ceases to amaze). Shots I'd have missed two years ago I'm getting now. I still miss plenty but its not because of the equipment any longer. I'm sure something will come along that will be even better at some point, but I honestly don't know what I'd ask for or hope for that isn't available today, at least in m43 - I'm sure the sensors will continue to improve but that was never my primary issue, although I like the low light capability today.

So I don't think there's anything irrational about buying new gear when it provides something that the old gear didn't that matters to you. In the film days, there was very little change in gear over long periods of time. I started shooting in the late '60s and until auto-focus showed up in the mid-80s I don't remember anything I considered a huge change in cameras. In camera metering got better, aperture priority was nice when it showed up, for some people stuff like motor-drives made a big difference but I never wanted or need it. But the IQ was all about the lenses and the film - the bodies lasted forever.

But that's not true anymore. This stuff is changing fast and a LOT of the changes are meaningful and useful. And, of COURSE most great photographs in history were taken with far more limited gear, but the people that took 'em were using the best that was available for their needs at the time and we're not doing anything different today. But the technology has improved by leaps and bounds in the past several years and there's nothing wrong with staying more or less on top of it if you want to and it doesn't break the bank.

-Ray

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Olympus OMD EM5 with several lenses, Fuji X-Pro with three lenses, Ricoh GXR with one lens/sensor unit, Panasonic LX7...

A better comparison would be the 7D that came out in 2009 and actually has a larger VF than the 1Dm2, and is only .5 fps slower.

Older, 'obsolete' pro-DSLR's are a very good bargain right now for those who need the speed/build/DOF. I still use my 1Dm2 as a backup to my 7D for weddings, and recently picked up a 5D classic very cheaply to replace my even older 1Ds classic.