I noticed that. One of our users asked for a cover for Space Jam for Saturn. I was going to make it but I couldn't download the cover.
The 300 dpi versions are still on the site, they just no longer have links so they're hard to access. You can either edit the link address for the preview image on ratigators.com or use the Wayback Machine to find the link and view the current version.
Whilst I commended his ethos to getting everything scanned, I found the images so badly moired I couldn't really use them for making covers.
I agree that they are imperfect, but I'd rather make my personal covers with one of his scans than a pixelated image from Google that I have to stretch to twice its size to fit the template. But for making official covers for the main site, you're right, the moire effect is just too pronounced.
And the manual scans are far better than what can be found at replacementdocs, regardless.