The hack allow ENCRYPTED Mobi files to be read on the Kindle. So you can buy a DRM-protected mobi book and read it on Kindle.
Amazon can do a lot of money only from selling kindle, like Apple does with the iPod.
How do you load other eBooks onto the Kindle? Just add Amazon DRM.
Non-DRM Mobi books, like free e-books found online in Mobi format, or files you convert to Mobi files, are already supported on Kindle.