Depending on your playstyle, Dishonored will rely more heavily on CPU or GPU: play it super stealthy, combining together a lot of powers affecting your vision (such as Blink or Dark Vision) not to get caught, and you'll find yourself GPU bound pretty quickly on lower end cards. On the opposite, play it the brutal way, alerting and fighting every single AI on a map at the same time, and your CPU will suffer, especially if the game runs with 2 threads only.

The min spec were quite high on purpose, so that people experience a constantly smooth and stable game. Most of the time, the game will run great on lower systems for sure - especially if you give a try to lower display resolutions such as 1280x720 (720p) or 1280x800 - but you may experience framerate drops in some spots, which might end up hurting your gaming experience.

Edit: Our goal was to ensure 100% that if you have these specs, you will not only be able to launch the game but it will run smoothly on your PC. We're fighting against the legacy of min specs being the specs at which the game launches but then runs miserably for some of the users.