At least as this is software for developers, I reckon most won't mind buying it outside the appstore, it sounds really useful.
It works quite well for me.
I like to think this is a foulup and will be fixed soon. However, XCode 8's help system is massively improved and this might be a case of Apple trying to force developers down that route. Which is a bloody shame. I really hope this is just some screwup :(