ADO.NET, DataColumn, DefaultValue, Expression og DataGridView

Jeg har en DataTable med nogle kolonner i. Hver kolonne har en DefaultValue og nogle kolonner har en expression sat. Jeg viser nu DataTable i et DataGridView vha et DataView. Brugeren har rettighed til at addere i DataGridView'et.

Jeg ville nu formode at DefaultValue ville fremkomme i nye rows, men nej. Ydermere fungere expression ikke, HVORFOR? Her er min kode:

DataTable dt = new DataTable();

dt.Columns.Add(CreateColumn("d", typeof(string), null, ""));
dt.Columns.Add(CreateColumn("a", typeof(string), null, "0"));
dt.Columns.Add(CreateColumn("b", typeof(string), null, "0"));
dt.Columns.Add(CreateColumn("c", typeof(string), "CONVERT(CONVERT(a, 'System.Decimal') * CONVERT(b, 'System.Decimal'), 'System.String')", "0"));

DataView dw = new DataView(dt);

this.dataGridView1.AutoGenerateColumns = false;
this.dataGridView1.Columns.Add(CreateDGColumn(new EPBC.Windows.Controls.DataGridViewTextBoxColumn2(), "d", 0));
this.dataGridView1.Columns.Add(CreateDGColumn(new EPBC.Windows.Controls.DataGridViewTextBoxColumn2(), "a", 1));
this.dataGridView1.Columns.Add(CreateDGColumn(new EPBC.Windows.Controls.DataGridViewTextBoxColumn2(), "b", 2));
this.dataGridView1.Columns.Add(CreateDGColumn(new EPBC.Windows.Controls.DataGridViewTextBoxColumn2(), "c", 3));

this.dataGridView1.DataSource = dw;

private DataGridViewColumn CreateDGColumn(DataGridViewColumn column, string headerText, int index)
{
    column.DisplayIndex = index;
    column.AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
    column.HeaderText = headerText;

    return column;
}

private DataColumn CreateColumn(string name, Type dataType, string expression, object defaultValue)
{
    DataColumn dc = new DataColumn(name);
    dc.DataType = dataType;
    dc.Expression = expression;
    dc.DefaultValue = defaultValue;
    return dc;
}