I'll admit that you make a convincing point. My main concern is wether or not I should continue investing in Canon glass with the eventual plan of buying a 5D III when for the first time a Nikon camera has made me question my loyalty to the EOS system. Despite the fact that I still see the D800 as a more advanced camera (the Ivy Bridge to Canon's Sandy Bridge, to continue your computer analogy), I've heard enough today to be reassured.
I agree that the D800 has a more advanced
sensor - but I'd argue that doesn't make it a more advanced camera. The 5DIII has 6 fps (vs. 4 fps, 6 fps is achieved only in DX mode and then only with buying the grip, AFAIK), and has 2 stops higher native and expanded ISO settings. The 5DIII has a better AF system, but less advanced metering system. Overall, I think the 5DIII is a better general purpose camera, while the D800 is better for still/studio work, provided you have top lenses to match the sensor (even the 14-24mm seems softer than I'd want in the corners on the D800 - the high pixel density is exposing a weakness in what is an otherwise excellent lens).
The cost of changing systems is pretty significant - a lot of lost $ on the same of your Canon lenses, compared to the cost of purchasing Nikon replacements (and most of the Nikon counterparts are more expensive - sometimes substantially more expensive). New flash(es), accessories like wireless triggers, etc. I do know at least one photographer whom I respect that did switch to Nikon for the D800, it really depends on how strongly you feel about it.
