There were many years during which the only known way to decrypt Audible books was by burning CD's and ripping them back, or exploiting the analog loophole. The encryption may have been standard, but no one had figured it out, and it's not as though Audible told anyone what to do.

Again, it's great that we now know how the encryption works, and everyone should go ahead and decrypt their books. But DVD's aren't DRM Free just because the encryption format was broken a long ago.

Furthermore, Audible's usage terms do restrict you from decrypting your audiobooks! Whether you want to abide by them are of course up to you.