The definition as surmissed by sociology, as soft science, has religion as a more concrete social/cultural structure. Which means the side of personal beleifs is not included because that is considered biased, and that skews scientific definitions and results. But on the personal side a persons beliefs could very well be seen as a religion. Even if a "religion" isn't followed. I suspect religion would be defined differently in psychology as well!
Perhaps trying to view anothers veiwpoint from both sides would help. The personal is as relevent as the sociological, and visa versa!!