Well, just re-read the question. It doesn't get more straightforward:
What makes other games have 'proper' HDR and why AW is lacking?
Notice the words what and why. Is the lighting of UC2 (or any other game PS3 game you wanna put in here) 128-bit while AW is 16-bit? Or is UC2 FP16 while AW is FP10? What?
Note that I made up those numbers, I myself have no idea what they really are.. But, that's the kind of detail I'm looking for. Since I don't know, and you apparently do, I would like some light in this darkness, figuratively speaking...
Truth does not fear investigation