Yes that's exactly what I'm referring to, because I know that they have one but they don't seem to store this during their GBuffer pass.
I guess since they're using a light-pre-pass design they might do that at the second geometry pass but they don't mention that anywhere.
Also here on page 29 http://www.unrealengine.com/files/misc/The_Technology_Behind_the_Elemental_Demo_16x9_(2).pdfthey show their gbuffer layout which also does not feature velocity, same thing happening with frostbite 2

you simply use the depthbuffer from the gbuffer-pass to generate a velocity buffer for all static elements, afterwards you render those few moving objects on top.

I see, so that means I'd have to sort objects between static and dynamic, right ?

well, there are not really any obvious alternatives to that, I'd say. (btw. you don't want to seperate dynamic/static, but moving vs none-moving objects. dynamic objects that don't move, might also not need to be rendered).

From what I remember (which may be incorrect), everything in crysis is treated as a non-moving object as far as motion-blur is concerned except for the first-person gun model.

So besides the gun, everything gets its velocity vector from just depth + two view-proj matrices, while the gun renders out velocity vectors to a g-buffer.

http://mycryengine.com/index.php?conid=8

"Motion blur can be applied both to individual objects (object-based motion blur) and to an entire scene (screen-based motion blur)," :)

not a good pic, but I think you can see object motion blur on the moving alien

http://www.abload.de/img/vlcsnap-2012-04-24-236zrdg.png

so I think it's the other way around. there is really object motion blur on moving objects, but the first person weapon has no motion blur, as it's bound to your head, if it would start to blur while moving, it would rather look like you're on drugs than a directional blur due to motion.

I see, thanks a lot.