Windsor6,
If you travel often, watch from the comfort of the terminal, a pilots "walk around". The difference between a dry day and when it is raining is extreme in terms of ground travelled on a walk around, from the operators that I have witnessed. I really wonder how much is "observed/discovered" on a rainy day walk around. Food for thought....draw your own conclusions. PS....not tarring all pilots with the one brush, but some just don't like getting wet !