Forget about inflation, exchange rates, and all that. Those are all excuses. The 5D3 doesn't have to compete with a 5D2 released at $2700 4 years ago. It has to compete with the D800, which has a much better sensor and sells for $3000.
Right, it does have to compete against the D800, which was priced lower at introduction. Happily, the 5D3 price is coming down.
However, the question of a "better sensor" depends on the intended use and the preferences of the user. I prefer Canon color for photos of people, so the 5D3 has the better sensor for me
. If I were a landscape photographer, I'd probably favor the D800 sensor.
And other important factors come into the equation. Without a smaller Raw file format and without a super-quiet shutter mode and without Canon ergonomics and certain Canon lenses and the Canon radio-controlled flash, the D800 is less attractive for me
, and therefor less competitive even at a lower price. For these reasons, the 5D3 competes very well for some photographers, whether priced the same as the D800 or higher. It comes down to the needs and preferences of the photographer.
So there are multiple factors, some of which have greater importance to certain photographers; DR is just one of them. Back when Nikon didn't offer a full-frame camera or any camera with excellent high ISO performance, some photographers still preferred Nikon because other factors were more important to them. This is why reducing camera competitiveness to just one or two factors and a price doesn't work.
There are obviously many photographers for whom the D800 will be a better fit and likewise many for whom the 5D3 will be a better fit, notwithstanding any price differences. It's apparent that Canon and Nikon intentionally design at least some of their products with somewhat different buyers in mind (with a good deal of overlap, of course) — this way they don't have to compete strictly on price.