Just another post to point out that I have used the SB-26 directly on a D70 in Auto mode as well.
When you set the ISO and aperture up nicely, there's no difference in exposure between SB-800 and SB-26 or any other speedlight, for that matter.
The main advantage of i-TTL (or TTL for old film+speedlights) was the speed and automatic exposure calculation due to the speedlight and camera being aware of each other's settings as well as the lens settings (e.g. D lens communicate distance information).
In Auto mode, it's basically down to the photographer to change the speedlight setting everytime the camera setting changes... and reviewing the exposure before adjusting the speedlight settings again.