For one thing, I suppose, the etymology of "informatics" explains part of it. The "-ics" ending means "the science of." So "informatics" is the science of information rather than the management of information.
The Wikipedia article defines "health informatics" as having these key aspects:
- Architecture for electronic medical records and other health information systems
- Clinical and other health related decision support systems
- Standards for integration
- Standards for terminology and vocabulary
Food for thought - In the health care industry, does it make sense to co-locate business roles like master data management, data quality, information integration, and business intelligence with the traditional informatics departments; rather than building them within business management units or IT/IS units? Does asking health informatics to work with other non-clinical business functions somehow risk or distract from patient care responsibilities?
(As a side note for those across the pond, it turns out that "business informatics" is a European term, closely related to "information systems" study, but with some subjective differences pointed out in the Wikipedia article. It is not a term commonly used in the U.S.)