A possible reason it doesn't use standard tabs is that it began this way; v3.8 versions.txt:
Quote:
51.The Options dialog now uses Tabs. I had trouble using
existing TabDialog DLL's, so I coded my own Tab
display routines.


I guess the migration to the standard win32 tab control never happened. I agree that this migration should gradually take place, not just for tabs but for most non-standard controls, especially those in the main GUI.