Here's what I suggest: Add an official module that displays module info on it's own seperate page. It would be essentially a public version of the Admin modules listing, displaying information supplied by the various version.php files already supplied by the modules.
I'm not sure what the implications of modules already written are; many require the developer info be included in the footer, but could that mean the PostNuke footer as opposed to the module footer? Even if not, it could be official PostNuke policy to encourage developers to allow module credit being displayed through the credits module.
It seems to me that a credits module would serve everybody's needs; the interface would be clean, interested parties could find developer info in a standardized place, and developers could get the work out.