I'm not sure any Nikon announcement would really be a motive. How many people are sitting out there with no Nikon or Canon lenses, waiting for February to see which system to buy into?
Just about everyone who might be interested in a $2500-$3000 DSLR will already be pretty heavily invested in either Nikon or Canon gear and very few of them would want to take the financial hit of switching systems. Whoever is "ahead" at any given time will be "behind" after their competitor releases their next camera, so switching is generally pretty pointless anyway. Most sensible photographers buy into Nikon or Canon and stick with their choice. It's not like there is a huge "night and day" difference between systems anyway.
The 5D MkII price was due to fall, as do all camera prices some time after the initial demand drops a bit. The 7D is taking it's time, but prices on that should start to drop a bit fairly soon.
Adorama have the
5D MkII for $2499.00B&H have the
5D MkII for $2499.95 and that includes a shoulder bag and two 4GB CF cards