IPolygon5 interface does not inherit the IPolygon4-members

Discussion created by dpalmetz on Sep 6, 2012
With ArcObjects 10.0 exists the IPolygon5-interface that holds only one member: IsEnvelope. It does not inherit all the members from IPolygon4.
The IPolygon4-interface does inherit all the members from IPolygon, IPolygon2, IPolygon3. It is surely not a big deal to get the IPolygon5-interface of an object, but is nasty and unnecessary code.
Is there any reason that the IPolygon5-interface does not inherit the members from IPolygon4 (despite the members of IPolycurve, ICurve and IGeometry)?