There are a few theories on why wings work the way they do and even though Rich speaks in absolutes, we aren't absolutely certain which theory is correct. The Bernoulli theory is still widely accepted but it isn't as easy to apply to computational fluid dynamics so the Kutta-Joukowski theorem, which is easier to follow mathematically has gained in popularity. The reality is that many experiments have been done supporting the Bernoulli theory. I've even done some myself. And yes, viscosity plays an important role in lift as well as drag