int[] source = new int[]{1,2,3,4,5,6};

List<int> list = new List<int>( source );

Debug.Assert( ((IList<int>)list).IsReadOnly == false ); // false

Collection<int> collection = new Collection<int>( source );

Debug.Assert(  ((IList<int>)collection).IsReadOnly == true ); // true!!

When the documentation says 'wrapper' they really mean it.