Maybe your particular version of wget does not like the fact that builds.openmpt.org uses a different SSL certificate than buildbot.openmpt.org, because both domains are hosted on different servers. Or the IdenTrust root certificate is missing in that wget version.
Like manx, I cannot reproduce the problem with wget 1.18.
Edit: builds.openmpt.org runs on my own server which deploys a more modern HTTPS configuration than openmpt.org and thus fails on some older clients. But even Internet Explorer on Windows 7 can connect to it here. On Windows XP you will be out of luck with Internet Explorer, though.