I know supply is limited for both cameras because neither Canon or Nikon can get enough cameras out of the gates to satisfy their customers, but anyway...
my theory is that, once manufacturing issues are solved, Canon will have to lower the price of their 5D3 because of low sales numbers, given that the D800 is so much better for stills in nearly every image quality metric, and its price is significantly lower too
it's happened before, in the 5D2 vs D700 battle, and in the D7000 vs 60D battle:
* July 2008: Nikon launches D700 at $3000
* Sep 2008: Canon launches much better 5D2 at $2700
* Dec 2008: D700 has fallen to $2320, 5D2 still $2700
http://camelcamelcamel.com/Nikon-12-1MP-FX-Format-Digital-3-0-Inch/product/B001BTCSI6http://camelcamelcamel.com/Canon-21-1MP-Frame-Digital-Camera/product/B001G5ZTLSaug-2010: Canon launches 60D at $1400
sep-2010: Nikon launches D7000 at $1200; it's better in some areas (noise, DR, color) but worse in others (mpix, video, swivel screen)
oct-2010: 60D has fallen to $1250, D7000 remains at $1200
since jan-2011: 60D almost always cheaper than D7000
http://camelcamelcamel.com/Canon-60D-3-0-Inch-18-135mm-Standard/product/B0040JHVC2http://camelcamelcamel.com/Nikon-16-2MP-DX-Format-Digital-3-0-Inch/product/B0042X9LC4so, here is amazon's list of best selling DSLRs
http://www.amazon.com/Best-Sellers-Camera-Photo-Digital-SLR-Cameras/zgbs/photo/3017941when it started shipping, the D800 spent about a week in the top position, even if they never actually had it in stock
in the last week, the D800 has been hovering at 4th-5th, while the 5D3 climbed from 18th to 9th, and is back down to 16th now