As I understand it (from documentation only) the Operator Information Area is exclusively system controlled and features its own characters/glyphs, which are not available for general use. Like a status line, it reflects the state of the system, keyboard modes, and so on, and is distinct from the general use area. So it's pretty much the same as a hardware controlled status line, but for a complex system.

BTW, another, entirely different point may have been in what we may call "compatible appearances" (somewhat related to UX): meaning, even if it was about entirely different software, written especially for the PC, IBM may have still preferred to provide this in a format already established by their existing terminals and the software running on those.