Plug-ins only load in the version of Rhino they were built against or newer. For example, if you build you plug-in against Rhino 5 SR12, it will load in SR13 and SR14. But it will not load in SR11, SR10, etc.
This should not be a problem for anyone, especially those who run the Fooo4Rhino site, as there are plug-in on the site that have Rhino version requirements. Here is one, for example:
Perhaps your page on Food4Rhino should state the Rhino requirement?