Hey, Sorry for the title. I just wanted a bit of attention. But really, your update system isn't the most convenient. Even I was able to make a premium plugin that supports one-click, automatic WordPress updates. Here's how.
White Shadow made a class that makes this a breeze. With this class, WPMU DEV's updates will show as notifications just like any other WordPress plugin. The class also supports authenticated updates. Please use it and make updates easier for your premium users. Thanks!