Well in Crysis, the picture on the 8800 isn't as good because when they disigned the drivers, they made them look for a program called "crysis.exe", if it was found running, then the drivers would cut the quality in the game, to make up for more fps. This can be remedied by renaming crysis.exe to something else, like cup.exe or something... There is no telling that nvidia will do this with future games though...
As you said, 2-10fps isn't that great, but in games like Crysis it does count. However, if you were to rename crysis.exe to something else, you could expect a fps drop, and the 8800GT would perform closer to the 3870.