Product vs Core. Why use low level API ?

Sometimes I wish that product API would not raise errors, but just return numeric result with the error number. This is what happening in the core API.

For example, the W6PTimeIntervals is a simple product wrapper for the W6TimeIntervals core class. Interesting is the fact that W6TimeInterval is a core class, which is used in the product without a wrapper.

However, the following short example of code is an implementation of a method, which is sometimes needed when dealing with time intervals. The error handling is general and there is no need to deal with "end of list" error:

Private Sub UnSetTimeIntervals( _
 ByVal intervals As W6PTimeIntervals, _
 ByVal unset As W6PTimeIntervals)

  Try
    Dim W6RC_MDL_TIME_INTERVALS_END_OF_LIST _
      As Integer = 4120

    Dim rc As Integer = 0

    Dim timeInterval As W6TimeInterval 
      = New W6TimeInterval

    ' UnSet older intervals from the newer intervals,
    ' so only the new interval remains
    rc = unset.RefW6TimeIntervals.GetFirst( _
     timeInterval)

    Do While (CatchRcExclude(rc, _
     W6RC_MDL_TIME_INTERVALS_END_OF_LIST))

      CatchRC( _
       intervals.RefW6TimeIntervals.UnSetTimeInterval _
       (timeInterval))

      rc = unset.RefW6TimeIntervals.GetNext( _
       timeInterval)

    Loop
    
  Catch ex As Exception
    Call GeneralErrorHandling("UnSetTimeIntervals")
  End Try
End Sub

Private Function CatchRcExclude( _
 ByVal rc As Integer, _
 ByVal exclude As Integer) As Boolean

  If (rc = exclude) Then Return False
  CatchRC(rc)

  Return True
End Function

Private Sub CatchRC(ByVal rc As Integer)

  If (rc = 0) Then Exit Sub

  Dim errObject As W6ShPError = _
   W6ShPErrorUtilities.W6CreateCoreError( _
   rc, "", True, True)
End Sub