[CONNECT .NET] CurveVector and DgnCurveVector

The .NET API provides classes CurveVector and DgnCurveVector. CurveVector is analogous to the C++ equivalent, but DgnCurveVector is unique to the BentleyGeometryNet API.

DgnCurveVector inherits from CurveVector and some other interfaces.  What is its purpose?  Why doesn't C++ have a DgnCurveVector?