User blog comment:PlaguedWings/Demon's Souls 2: a fun little thought/@comment-6003396-20140115103409/@comment-6003396-20140116205242

Both Demon's Souls and Dark Souls were developed by From, and directed by the same person, Miyazaki Hidetaka. Atlus only published Demon's Souls in North America. Game publishers are very similar to book publishers, they are responsible for marketing and manufacturing the physical product, and they usually have little say in development. So if From/Miyazaki have said that the worlds aren't related, then the worlds aren't related.