I'm sure i once read an article talking about NV and AMD releasing deliberately bad drivers at launch and then making incremental improvements over the life cycle of the product to give it perceived added value. It obviously doesn't work, but i can see where they are coming from, from a purely business point of view.
Since most video card reviews are done on the day the card is released, it is in the best interest of the card maker to have the best possible drivers available at that time.
On a related note, I think reviewers should re-bench the HD6850 and HD6870 (among others) that were released with drivers that incorporated Image Quality Hacks that improved performance by 6-10% at the expense of image quality. Most of these hacks have subsequently been removed from the latest drivers, but those original performance benches are still the ones being used for most comparisons. http://www.tomshardware.com/reviews/geforce-gtx-570-gf110-performance,2806-5.html