This question came up with a client this morning, which is the first time I have had to answer it but it’s a very straightforward issue.
What if one is trying to use TMG to publish a SharePoint environment for both HTTP and HTTP access, while the certificate is appropriately setup in the SharePoint server it is not desirable to have the web publishing rule bound to the certificate, i.e. certificate stuff should be handled by the SharePoint environment. So, breaking the question down even more, they wanted to publish the HTTPS SharePoint instance WITHOUT using the certificate in the TMG instance.
This obviously is not a supported route, because logically it doesn’t make a ton of sense. One can’t use a HTTP web publishing rule without having the appropriate certificate accessibly and appropriately in place, and clearly is not a TMG limitation because it is the same requirement for ISA and Proxy Server stuff.