I could not add a comment to that blog, so I will do it here.
Please perform an experiment. Put any exe file on your HTTPS server with a valid certificate. Make an HTML page that links to it, put it on the same HTTPS server. Visit that page using Internet Explorer. Click on the link. Result: with some IE versions, you can't run the program. Details: http://answers.microsoft.com/en-us/ie/forum/ie9-windows_7/why-cant-i-download-files-using-ie9/d012bc50-786e-e011-8dfc-68b599b31bf5
That's why Windows software is always offered via plain HTTP URLs.
A more relevant question would be whether putty.exe or its installer is signed the way Microsoft allows exe files to be signed. Answer: no, these files are not signed.