Did you read what the author wrote about that?
Mostly decided for actual buttons because that's the way the user is informed of a way to initiate an action. It's more explicit than a link. (Part due to the hover-over effect as you mentioned, which looked ugly on a label.)
The ideal solution would probably be to integrate link support in CText.cpp, or even downloading the terms from the server and displaying them locally, if we can rule out security risks and persistence of the url.