Further to the excellent information provided by Transitional Man...
Harvey Fletcher once said "Stereophonic systems do not consist of two, three, or any other fixed number of channels. There must be sufficient of these to give a good illusion of an infinite number." Believe me, I think he knew what he was talking about.
In fact, During the 1930s, Fletcher, Blumlein and others filed a series of patents or invented equipment for the storage and reproduction of multi channel sound. Blumlein registered a patent for stereo recording on phonographs within the same year that Fletcher demonstrated using three channel sound. Three channel optical recordings on film strips predated stereo ones.
Since that time, Cinemascope, Perspecta, Cinerama and a host of other mulitchannel recording / encoding schemes were invented for theater applications, all the way up to modern SDDS, DTS and Dolby Digital. While (most) theaters could keep up, cost and technological limitations kept the older technology out of the home. Since consumer equipment was at most in stereo, there was never a need for more elaborate recordings.
Even as the technology became more available and affordable, the saturation of stereo equipment further alienated multichannel sound. TVs, walkmans and car audio were all stereo at most. There were no advantages to producing multichannel music recordings since the average customer would not be willing to upgrade all of their equipment and their software (tapes and cds) to newer formats simply to gain additional audio tracks. For most people, stereo was "good enough." For some people, mono, linear VHS audio recorded in EP and played through a TV speaker is good enough. There is no God
As Transitional Man pointed out, the big hurdle for 5.1 is cost. I can attest to the fact that once you invest enough money in a good 5.1 system, there is no turning back. The first time that I heard the guy whistle towards the end of Home on Cheryl Crow's Rockin the Globe DVD in DTS I was startled. Especially since it felt like he was behind me in row G and a little to the left! That is imaging and a very impressive sound stage. This is by no means on a spectacular system either: roughly $5,000 ($5500 counting cables, TV not included) of equipment carefully placed and calibrated, playing some very fine source software. All it needed was a little love.
Now that DTS and Dolby Digital are becoming more commonplace, and more and more consumers upgrade to enjoy these formats for movies, it becomes worthwhile for the music industry to record in more than 2 channels. The number of music DVDs, either concert or otherwise, have increased exponentially in the past couple of years. As this happens, the quality and quantity of 5.1 recordings will increase.
In the meantime, you'll have to pry my DTS copy of Diana Krall's Love Scenes from my cold, dead fingers.