A major complaint since launch has been the difficulty of figuring out if an item on the auction house is an upgrade or not. Blizzard plans to address this in a future patch.
It may not sound hard, but it isn’t an easy code change. It often takes a great deal of work in order to update and alter our complex coding, and it’s actually been a notable tech investment to try to tackle this particular request for updated item comparison tooltips (which Lylirra mentioned here as well). The good news is that we’ve been making a lot of progress, and this feature is planned for an upcoming patch. :)
Game designer Travis Day mentioned on the official forums that gear customization is a planned feature.