For first-person shooters and similarily twitchy third-person action games I agree with you that robust mouse/keyboard implementation on PC is vastly preferable to plugging in a gamepad. In this specific case, however, it's worth keeping in mind that Demon's Souls/Dark Souls are slow-paced melee-heavy games with "lock on target" functionality and with world exploration elements which pretty much require precise and seamless movement (for example, gently nudging the analog sticks on the gamepad in order to navigate the character on narrow ledges perilously close to bottomless chasms etc.). I honestly can't see this kind of gameplay working satisfactorily with PC-exclusive control setups no matter how good the port is.
Like it or not, gamepads have become a well-established standard on PC by now and unlike Dead Island (which was criticized for controller-exclusive manual aim options), I think Dark Souls' controller-oriented gameplay should make sense even for keyboard purists. There's a learning curve involved if you're unaccustomed to it, sure, but mere unfamiliarity with gamepads is something everyone can overcome.