Hardware utilization of Directsound3D was killed in Vista like another user had stated. After that there was more of a combined market shift with consoles and what not. Not many embraced the OpenAL container.
EAX used in games was more pre defined reverb in certain areas of 3D maps. The sound would practically change and adapt to environment unlike dolby where everything is mostly reverb 24/7...
Regardless, Call of Duty 1 and 2 only mixed Stereo at 44khz. CMSS-3D (which still works) emulates a surround feeling from basic 2 channel to altetnative sources. Unlike DH where most of the benefit comes from predefined multichannel settings.
The basic soundscape of the original 2 call of duty games is just very very good... Even mixed with miles 2D positional audio. (Also used in Source engine)