As I see it, Firefox links to CX because CX enhances Firefox - it allows FF to run plugins that it could not otherwise run.
*IF* Firefox enhanced Wine - by providing an MSHTML-compatible object, for example - then it would make sense to provide a link, as then FF would enhance Wine.
But FF does not directly enhance Wine, then there is no symmetry between the two examples, so using the FF example to justify WineHQ having a Get FF button is invalid.
This does not mean there are no other reasons to have a Get FF button, however.