Why is it necessary to add "default.aspx" to the URL?

I have "default.aspx" set as my default initial page; so why do I need to browse to:

www.knowitallsports.com/default.aspx to see my site? Shouldn't www.knowitallsports.com be enough?

Not only on my own (dev) machine, but from another machine here on the network, that is what must be done, otherwise I see discountasp.net's index.htm page.

?

 

It works fine outside of the building (don't need to add "default.aspx"). Don't know why...

 

My guess is that it has to do with the "White List" IP address. If your Dev machine is part of a network, and you tried from another machine within your network, your outside IP address will be the same on both machines, regardless of the internal/private IP address... i may be very wrong on this matter, but i though i would give it a guess .