After a few moments of searching I'm going to assume that whoever specifically scraped and uploaded the page may have removed the adsense javascript. Doesn't look to be a normal archive.org thing.
I checked some other site and the Adsense code is not changed by archive.org. So something is strange.
Maybe Gwern experimented with different types of ads and on that page at that time did not use adsense?
I do see the adsense code in a snapshot from a year later:
http://web.archive.org/web/20160629230243/https://www.gwern....