Choc,
Your wife knows that you used to be unhappy and that you, without explanation, stopped saying anything about it.

So she probably assumes that you came to terms with the situation, have accepted her as is and decided that you are ok with the status quo.

Why would she think otherwise? Sure she knows she is not a "wife" to you, but she also sees a relatively happy guy living with her, being nice to her, taking care of the kids..essentially a person who is content with their life. Denial is a very powerful thing and while she knows at some level that you don't like your life this way, she has NO IDEA the extent of your unhappiness. She sees a guy who has seemingly come to terms with a sexless life and she is okay with that.
She misses the feeling of knowing that she is desirable but she is too shy/awkward/insecure/proud to say anything. She figures "If he thinks he's going to smoke me out, he's wrong. I can outlast him anyday."

I find your sitch so tragic. Two people who could really have an outstanding M are mired in an unspoken war.