@wellsriley blogged this year about an eleventh principal -- Good Design is Iterative (blog.wells.ee). I agree that this principal works in combination with the other ten principles, but not in isolation. For example, SaaS software gives the possibility of incremental enhancements that can enhance the user experience. However, that can also allow software that perpetually disrupts the user experience if new features are introduced that don't fit well into the existing user experience or if something in the software is refactored in order to improve it. Good design would easily accomodate new features without disrupting the user experience.