From Software would also like to remind us that the game has absolutely nothing to do with Demon's Souls. We're really not sure they're kidding anyone.
The name change seems to be a way for From Software to get out of PS3 exclusivity. From what we understand, SCEJ helped fund the original Demon's Souls which became a sleeper-hit worldwide. Dark Soul will launch on the XBOX 360 too, and will not use the same story or universe as Demon's Souls.
That's not really stopping the game from sounding like Demon's Souls though. According to a write-up in Famitsu magazine, Dark Soul will be set in a "medieval dark fantasy" world with themes such as "kings and knights". So it's Demon's Souls then? Ok.