From the "iTunes -- is there anything it can't do?" Department: a while back, I downloaded the Fats Domino song "I Want to Walk You Home" from the iTunes music store and was disappointed to discover that the track was presented as if it were stereo when in fact it was a two-track recording obviously never meant for stereo. Allow me to explain. Back in the 50s, it became customary in the recording studio to record songs intended to be released on 45 rpm records with two tracks: one for the vocal, one for the instruments (of course, nowadays, there can be many, many tracks), which were then mixed by the producer for the final mono version of the song for the 45. Until the late 60s, nearly all 45s were released in mono, not stereo; the idea of the two tracks was merely to improve the recording and mixing process: to avoid re-doing everything if there was a mistake in either the vocal or the music, and to make sure the instruments didn't drown out the vocal, as could happen if it were all recorded through one microphone. The intent of having two separate tracks was not to create a stereo recording. They could be mixed to create a stereo track. Until the late 60s however, mono was a much more important medium than stereo in rock and pop, mainly due to the importance of the 45 rpm single relative to the more "adult" stereo LP. Singles were carefully mixed in mono to make the maximum noisy impact from a single speaker (a "wall of sound," to coin a phrase) and then, as an afterthought, if at all, mixed for more sedate stereo. For example, the Beatles and their producer George Martin, until the final triumph of stereo in '68-'69, lavished much more attention on the mono mixes, as did Berry Gordy at Motown, where the stereo mixes of songs were slapped together by engineers working the night shift. (Much of the above factual background, when not based on general knowledge or the evidence of my own ears, is based on the book 45 RPM: the History, Heroes, and Villains of a Pop Music Revolution and, as to the Beatles, on Mark Lewisohn's excellent The Complete Beatles Recording Sessions. For more, much more, on the Beatles from the standpoint of stereo vs. mono recordings, this article just about covers it.)
In the vinyl record era, 45 RPM singles usually stayed in print where there was any demand for the song. In the CD and mp3 era, however, vinyl went bye-bye and many 50s and 60s recordings became available only in their inferior stereo versions. Apparently, the record companies must cater to the same type of taste that views all black & white movies as inferior to color. (Check out this compilation of 60s hits, where one of the supposed selling points is that it contains stereo rather than mono versions of the songs.) The original, preferable, mono versions of 50s and 60s songs are tough to find. Only rarely will iTunes specifically list a track as the "Mono Single Version." EMI has made the original mono versions of most of the Beatles' singles available only in a prohibitively expensive box set. Think of that: the most popular rock act ever, and some of their most popular songs cannot be easily heard the way they were originally heard (and were intended by the group to be heard).