They aren't remaking levels from scratch. They aren't creating models from scratch. They aren't even creating new textures, except for the (scant) new content. It's an HD texture pack and some new lighting in existing levels.
Top is the new version. Bottom is the old version (downsampled from 1800p).
What here justifies splitting the playerbase? What here couldn't given in a downloadable patch? What here prevents player save file migration?
Because this seems like a financial decision, not an engineering one.
As users we make make concessions for the financial needs of companies. After all, this is a business as well as a hobby. This is bald faced, though. It's rude, after putting out one of the worst ports in years with Dark Souls, with little after-release support, after selling Dark Souls 2 for $59.99 with promises of no DLC, then DLC for $24.99 (good or not). This is the kind of stuff other companies put out for free on PC. If there isn't a steep, steep loyalty discount (like, $10-$15 max), then Namco deserves all the criticism it gets.
On the positive side, the "DX 11" version doesn't look worth losing sleep over for those who already own the game, who can mod it with GeDoSaTo, texture replacements, and lighting mods. I also suspect that shortly after DS2 DX 11 is released, most of the graphics changes (not the content additions) will find their way to the DX 9 version in mod form.