KimE, Aye, polycotton trousers can get wet but if firms such as Craghoppers & Fjallraven have such good reputations it's because, I would think, that they're using tried and tested material. In fjallraven's case, they sell a wax that can proof their outer wear to a certain degree. They point out, however, that the more wax that is used, the less breathable is the outer wear.
The original point oif the post was that baselayers are not the best choice for walking because of their capacity to hold water. It wasn't to say don't wear any cotton in an outer layer.
The choice of whether to bring waterproofs with you, depends on the walker but, generally, waterproofs protect the walker from losing body heat.I certainly wouldn't want to be out in the hills in any trousers without waterproofs to put over them, and definitely not in weather we're experiencing at present, even if they were made of a material that dries quickly once out of the rain.