The difference here is that instead of using forms, you use User Controls basically. We have a BasePage that has all of the same functionality as the BaseForm. So it isn't that hard of a move, you would be able to move your controls, code, etc. over from a dialog to an inherited BasePage. But like anything else, when you make a drastic change to the UI there is always a little elbow grease that has to go into it.
But this is something that we plan to offer in the future...standard dialog MDI interface (current logic) or our folder based MDI. This is why having our own large-scale commercial application is so good for SF....we go through the fire first