In a nutshell, TrueAudio is a return to the concept of hardware accelerated audio processing, with AMD leveraging their position to put the necessary hardware on the GPU. Hardware accelerated audio processing in the PC space essentially died with Windows Vista, which moved most of the Windows audio stack into software. Previously the stack was significantly implemented through drivers and as such various elements could be offloaded onto the sound card itself, which in the case of 3D audio meant having the audio card process and transform DirectSound 3D calls as it saw fit. However with Vista hardware processing and hardware access to those APIs was stripped, and combined with a general "good enough" mindset of software audio + Realtek audio codecs, the matter was essentially given up on.
Now even with the loss of traditional hardware acceleration due to Vista, you can still do advanced 3D audio and other effects in software by having the game engine itself do the work. However this is generally not something that's done, as game developers are hesitant to allocate valuable CPU time to audio and other effects that are difficult to demonstrate and sell. Further complicating this is of course the current generation consoles, which dedicate a relatively small portion of what are already pretty limited resources to audio processing. As a result the baseline for audio is at times an 8 year old console, or at best a conservative fraction of one CPU core.