Purple rhino questions

I really don't want to get caught in the controversy about whether  the purple rhino virtual gift is a Good Idea.  (I try to steer clear of the really world-shattering issues.)  But I'm puzzled.

What is this "forgotten" symbol of the Gay Rights Movement? 
Why have I never heard about it until now?  Ignorance?  Britishness?  (Rhinos failed to swim the Atlantic?)
Who thought it would make an inspiring symbol for gay people?
Why?
Why a rhino?
Is this all a wind up?
Why?
Why purple?

Is there any connection to the Purple Cow Poem?

And, finally... why?

Please help if you can!