Maybe you can see why I kind of have my doubts sometimes that any women are interested in sex at all!
Not really. Just as very few people are leg-less, very few women have zero sexual desire. Why extrapolate to all women from a sample size of one (your wife)?
The difference is you can see other people have legs. With sex, you only see the sex you have, and otherwise you just have to believe what other people tell you, and if there's one thing people are generally not totally honest about, it's their sex lives.