How many lights are used in MW, NWN and Doom 3? Remember JC optimises his games for best performance as well. I seriously wouldn't be surprised if D3's shadows take less of a hit than NWN or MW. I don't play with Shadows enabled in MW. Also the amount of objects casting a shadow will also vary so hence will the performance.
"Never before has any voice dared to utter the words of that tongue in Imladris, Mr. Anderson" - Elrond LOTR