I have a canon 550d rebel and was considering the "jump" to FF.
The Canon 6d is in my budget. However the Nikon D800 is available (refurb) for $2,300.
I ask myself - why spend almost the same on the inferior 6d ? Why does canon seem to give less and charge more ?
Because they can charge more and get away with it. They're in the market lead, know it, and act accordingly, much like Apple's been known to. They've managed to create a loyal fan base of repeat customers, originally by making the best hardware experience, again, sort of like Apple.
But unlike the computer biz, there are plenty more challengers in the camera biz. Nikon's certainly learned a few things over the years and 2012 has been a banner year for them putting out some wow products at wow price points. Unlike Canon's yawn products at OW price points lately.
Nikon's trying to offer more for less because they have
to try harder; they're still in 2nd place.
But to try answer your implied ?, which FF system you choose will depend on a lot of factors.
If you want to shoot low light, hi ISO, event sort of work, Canon's likely the better choice unless you step up to pro level bodies where either brand is near as good as the other.
If you prefer to shoot creative and landscape images at lower ISO, Nikon's raw files are more malleable in post without seeing the stripes of pattern noise most Canon cameras exhibit when raw files are pushed hard. Especially with pro-sumer and consumer level bodies.
Those refurb prices lately are a wicked deal!
I like my D800s more the more I use them but I'm still thinking of a 6d to replace my 5d2 for those few instances where I want to use my Canon glass instead of Nikon.
And, FWIW, I generally prefer Canon's lenses but there's no shortage of fine Nikon and 3rd party lenses that are up to the abilities of the D800's hi-rez sensor and they don't all cost as much as Canon's L-class either.
My kit's stuffed with great (used and new) F-mount lenses that cost me way less than my Canon gear and they perform well enough to please a technocrat like myself. My customers are far less particular.
File size complaints re the D800's raw files?... pointless. If you spend the $ on gear you have to realize you need a modern computer to keep up also.