Popular music studies is an interdisciplinary exercise.
Sociology, cultural studies, English, communications, musicology, music theory, ethnomusicology, anthropology -- these are some of the disciplines that have contributed to popular music studies.
But being interdisciplinary, as Stanley Fish once said, is so very hard to do.
At least part of the problem is that different disciplines come at any topic with their own strengths and weaknesses, and they tend to grab at topics which they can most easily explain. There are notable exceptions to this, but there seems to be a divide among the disciplines that do popular music studies, leading to very interesting musical divides. These, in turn, reflect social divides.
Take, for example, music theory's (and to a lesser degree, musicology's) contributions: the tendency has been to study popular song that has relatively complex forms and interesting chord progressions. Thus, progressive rock, psychedelic rock, the Beatles, and some of the more clever singer-songwriters have received significant attention. Heavy metal, too, has gotten its share of attention, with its modalities and virtuosic guitar solos providing fodder for analysis. Even recent work on girl groups draws off of a repertoire with some advanced compositional and arrangement techniques -- the world of the Brill Building and Motown was self-consciously professionalized, after all.
On the other side, consider cultural studies and sociology: their emphasis on working-class lifestyles and subcultures have led to revealing work on punk rock, the mods, the London rasta and rudie scene, and so on. Likewise, the interest in reading (postmodern) texts led to a flurry of studies on music video.
I'm obviously being reductive here to make a point, but I find it interesting how these two disciplinary areas have had little to say about musical topics across their divides. For example, in Frith and Horne's sociological book, Art into Pop, the authors stress in the introduction that this is about the role an education in fine arts had on musician-artists who ended up in popular music; they issue a stern caveat that they are not interested in so-called "art rock," that classically-influenced stuff that bands like ELP peddled. What follows is stuff like the Velvet Underground, Roxy Music, Talking Heads, PiL -- pop on the proto-punk/punk rock/new-wave axis.
On the other side of the divide, punk has gotten little musicological attention. In his seminal Rock: The Primary Text, musicologist Allan Moore dutifully (if briefly) surveys punk as a substyle of rock, only to dismiss it as something that will be seen as having had a limited stylistic influence on rock at large. (A speculation which I'm guessing was probably written around 1990, before alternative rock really took off -- the original book came out in 1993.)
I have to confess my own complicity in this divide: by writing about Rush, I was doing the musicological thing of diving into something that was self-consciously designed to be interesting to a certain kind of musician. Rush analyzes "well" musicologically. It's a convenient topic, from one standpoint.
What bears further thought is how the relationship between social divides and musical divides (which we are mostly aware of) also interrelates with disciplinary divides. Most of us working in popular music studies are striving to do interdisciplinary work, but each discipline carries its baggage.