Most downloaded title in the Million Book Project

Ha ha. While using the Million Book Project's page at the Internet Archive today, I noticed that the "Most Downloaded Items" sidebar supplies the following numbers:

1. Ethics Of Sex Acts: 9,177 downloads
2. Advanced English Grammar: 2,680 downloads
3. Brief History Of Mathematics: 2,355 downloads
4. Early Jazz: 2,157 downloads
5. The handbook of soap manufacture: 2,045 downloads

A book on sex is 300% more popular than Advanced English Grammar and Brief History Of Mathematics? Who'd have predicted that?