When you type a URL into your browser eg.
the server responds by sending back a default file,
which can be welcome.html, default.html, index.htm
or anything else the server is set up to respond with.
The browser then loads the page and displays the URL
that you originally typed in because that's what it's
programmed to do.
However, some search engines choose to display the
ACTUAL URL in the case of non-standard index files.
WebCrawler does this too I believe.
My overall response to your original question would be
"does it really matter?"