Audio codecs don't evolve in a vacuum. Take the changing interface for digital audio data, for instance. To date, the most popular standard for digital audio has been the Sony/Philips Digital Interface (S/PDIF), or IEC 60958-3. But Dolby Digital Plus will need the High-Definition Multimedia Interface (HDMI), a new standard that streams audio and video together.
Meanwhile, the number of audio channels for the surroundsound experience continues to inflate. The lowest-level surround systems are designated "5.1," indicating one central-channel speaker (generally optimized in the human vocal range, because the speakers to either side tend to leave a "hole" in the middle of the front wall, just where most movie dialogue takes place). There are also side and rear binaural speakers, plus an "effects" speaker to handle those sounds you feel with your gut more than you hear with your ears. Beyond 5.1, some systems come with even more speakers.
While many consumers who buy these systems may never take all of these speakers out of the box (sometimes spouses draw the line at organizing a room around a vast distribution of speakers and cables), the system must be designed for all those channels.