En tu TableModel, te falta decir que columnas pueden ser editadas.
Código:
/*
* Don't need to implement this method unless your table's
* editable.
*/
public boolean isCellEditable(int row, int col) {
//Note that the data/cell address is constant,
//no matter where the cell appears onscreen.
if (col < 4) {
return false;
} else {
return true;
}
}
Saludos.