Why don't all System.Web.UI.WebControl classes with Text properties implement ITextControl?

Question

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,

Answer 1

I think it was designed ok, I don't think it was an oversight; those are the controls where text is the primary focus of the purpose of the control. I do see your point because that would be very convenient to have controls utilize more of these types of interfaces.