It does support blur just not as an effect. It can be done through alpha images easily! Pure laziness or denial on someones part.

TBH I can't see a way to add blur through alpha images.

I think he's talking about using a blurred image overlay but that's already implemented (minus the blood drops).

Perhaps there could be a way to fake the motion blur using a broken shader.

There are water puddles on several custom maps using TC:E's original puddle shader (seen on northport) improperly.
If something moves in front of them, it leaves traces for a few seconds.
Same thing happens if you look at them and move the mouse around.

I have no idea if that kind of a broken shader can be used as an full screen overlay with the same effect though.