Well, at least in my area (it might be nation-wide?), it's illegal for a bicycle to ride on the interstate. Therefore most tourers really aren't going to run into a situation where cars are whizzing by at 65+mph. This holds true for most of the East coast. Out west, some states allow use or limited use of the interstate.

I like to stick to smaller roads and routes. One of the biggest factors that I consider when on a road is "is this the safest route." I've made stops (generally at bike stores when I see them), and ask them if there are better routes to my destination than the one that I have planned. I have yet to be led wrong by asking.

As far as not getting hit, it's the same train of though as to why people changing a flat on the shoulder don't get hit.