I can't read Japanese at all, but many people who've read the article seem to be pointing to that fact.
Specifically these lines:
Hopefully we have some people who can translate it, but man, things are just not looking bright for PC gamers, or even Dark Souls fans in general.
EDIT: this was just found: http://www.destructoid.com/dark-souls-pc-details-specs-control-pvp-and-more-225963.phtml
"Bad news for those hoping to see a high-resolution Dark Souls with this PC port: Miyazaki says that there will be no difference in visual quality between the PC and PS3 version"
UPDATE: Many people have pointed out that the 720p part refers to the TEXTURES and not the pixel resolution.