[plt-scheme] When does eqv? differ from eq? , from equal?

Woodhouse Gregory wrote:
> 
> I almost always perform tests with eq? or equal?, seldom (if ever) with 
> eqv? . The Reference is a bit mysterious, saying (in section 3.1)
<snip>

Can someone enlighten me about make-hash and make-hasheq?  It would seem 
that if eqv? is necessary, then make-hasheqv would also be necessary.

Or is it that the number and character distinction between eq? and eqv? 
is rarely needed in hashes?  Or am I missing something obvious?

Thanks,
Dave