This might have something to do with the way that name resolution worked inside of Sun at the time. If there was a host, say

    doppio.eng.sun.com

it would be referred to simply as "doppio" from within the engineering ("eng.sun.com") domain, or possibly as "doppio.eng" from other domains inside of Sun. It was fairly rare to use FQDNs inside of Sun to refer to other hosts inside of Sun. Thus, the following URLs all referred to the same resource:

    http://doppio/foo.html
    http://doppio.eng/foo.html
    http://doppio.eng.sun.com/foo.html

It's a plausible point of view that URL.equals() should report true for any two of the above URLs. (That doesn't mean that I think it was a good idea, though.)