Yes no doubt that familiarity will be a factor for some people and it is certainly a relevant consideration. I can actually appreciate this position because I choose a RRS BH-55 over a Markins M20 (despite it being more expensive and 2x as heavy/bulky) due to ergonomics alone. When it comes to cameras, I still think, perhaps wrongly, that people will look at image quality first and foremost, and the features on the camera that will result in better images in the circumstances in which they shoot. Right now, it is difficult to conceive of a situation (unless the Cam4800dx turns out to suck) that the D7000 won't have an advantage over the 300s when it comes to image quality.
I have actually said that I fully expect a new DX flagship (D400 or D9000 whatever they choose to call it) to be released by Nikon within the next year (if for no other reason then what I stated in my post, very few people imo are going to choose the 300s over the 7000 based on feature set and price, even if the 300s is priced slightly below the D7000). That being said the likelihood of the new model 'blowing away' the D7000 is slim to none imho. The D300s did not 'blow away' the D90 despite being released a year later. Further, the D7000 appears to have upgrades to all the major camera components that would impact image quality, sensor, AF module, meter, etc. Unlikely Nikon is going to significantly redesign these elements for a new DX model in the next year or two. The new DX flagship will certainly sell, but imo it will because feature set and image quality will be the equal of the D7000, plus it will have the ergonomics and build that people who like the bigger 'Pro' type bodies have come to know and love.