As an anthropologist, I find the more interesting question is why people are not compliant. My friend Ari Shapiro did an interesting study on this, noting that "Ethnography opens up the issue by entering the private space of pill-taking to understand the beliefs, relationships, and activities that contribute to patient (non-)compliance." The abstract for his paper is available at the EPIC website, but you have to be a member of Anthrosource to get the whole thing.
His study, as well as many articles in the popular media, point to the fact that compliance is about much more than remembering to take pills at the right time. Medications can make people feel awful, or look awful, or be unable to participate in important family events. Teenagers with cancer don't really believe they might die. The list goes on.
Interestingly, in my (admittedly very cursory) research, it looked like HIV/AIDS patients are a constituency which overall is very concerned with being compliant, but it is difficult because of all the cocktails and combinations of meds that must be taken at different times. I found several instances of people looking for community solutions (say text messaging each other) to help remember. I am not sure why this is different that other diseases (if in fact it is, or just a sampling error in my own research) but it is interesting nonetheless.