I do agree with you Paul, I rarely wear a waterproof around town and my thought process is nothing more waterproof than skin.
But there are times when you want to stay as dry as possible, ie. if you are stopping out overnight several nights, or temperatures drop/weather really changes and you are several hours from where you want to, then that's when you could encounter problem IMHO . Best be safe than sorry not to mention keeping all those waterproof clothing companies in business.
I've had my Salomon Cosmic 4d GTX for about 3 years and they are a great boot and worn them all day through wet conditions and have let me down - until early this year when I started to feel damp through them.
Personally, I blame myself for not looking after them properly, I tend to leave them to "dry out" then 2 weeks remember them and clean and proof.