I can only guess at Development's reasons for choosing that Next button, but I reckon it was to make apparent there's another screen of settings, just like the Next button in product settings. I agree it's a bit confusing in other ways, such as the fact that clicking Next in that case actually does save all changes on that first screen, whereas everywhere else the Next button doesn't save changes until you get to a Submit button that does, and the Submit button on the Rules screen only saves a new Rule. It would also have been better yet to have all the Shipping settings together on one, big screen rather than splitting it into two, but we were limited to the size of the Flash-based interface we already had.
At any rate, we've already been working on an HTML-based replacement for our current Flash-based Admin, so that will resolve many of our current usability concerns and allow ongoing updates, tweaks, and enhancements to the Admin interface much easier for us to implement quickly and more frequently. While the Flash approach was great for our Founder to develop a slick, attractive interface from scratch six years ago, it's become long in the tooth and increasingly challenging to modify at all, which is why we've been leaving the current Admin as-is and rolling all new features and interface fixes into the new Admin project.
Long story short: many good things are in the works that will come out all at once when the new Admin goes live soon, so thanks for sticking with us -- we'll make the wait worthwhile. :^)
