I'm curious why only some System.Web.UI.WebControl controls implement certain interfaces when they have the same properties of an interface.

For instance, there are plenty of controls that have a Text property but only the following implement ITextControl:

• Label
• Literal
• DataBoundLiteral
• TextBox
• ListControl

(TextBox and ListControl actually implement IEditableTextControl which implements ITextControl)

TableCell, Button, HyperLink and others don't so I have to write code like this

ITextControl textControl = control as ITextControl;
TableCell tableCell = control as TableCell;

if (textControl != null)
{
    textControl.Text = value;
}
else if (tableCell != null)
{
    tableCell.Text = value;
}

instead of this

control.Text = value;

Was this a design decision or an oversight?