Why is there advertisement on the automated update server? Why can't he just split them apart? What with things like Let's Encrypt nowadays, there really shouldn't be any excuse not to use https. Especially for a security related product!
So any possible attack against KeePass would as most cause the notification dialog to appear saying there's a new version.
anyway, the author found a solution by signing the text file that the update checker looks at. IMO, that's a superior solution to HTTPS. He's posted a statement on the KeePass website. http://keepass.info/help/kb/sec_issues.html#updsig