Paradigm, the center of the lane has the most oil on it (even though atmospheric crankcase ventilation is gone). Riding in the left 1/3 puts you in BOTH the drivers side and rear view mirrors for cars in front of you, as well as closer to the next lane over. Makes you more visible to the next lane over, also gives you more escape options should you need to go evasive. Same case on a two lane road. On a two-laner, the closer you are to the center the more visible you will be to entering traffic, and the more visibility you will have over the entire road. Think about a car coming out of a driveway with a huge tree at the end of it. That tree will most likely obstruct vision from the side of the road first... not where you want to be.
@KM I actually tend to get my thumb ready on the horn button before I pass a vehicle on the highway. I'm all about proactive safety. Doesn't always happen in the city if I'm using the clutch.
As for the pipes...
Yes, loud pipes have probably saved a few lives, but not in the context that is so commonly presented. Horns do work just as well, are not on all the time, and indicate emergency situations. Horns don't piss people off when properly used, and horns don't get the signs put up in some local neighborhoods here banning bikes with straight pipes.
If the point of loud pipes is safety, let me propose something. How about we increase the decibel limit of a bike for every piece of safety gear a rider has. If you wear a helmet, riding jacket, good gloves, good riding pants, good boots, reflective/bright overgarment such as a vest, or have added running lights or other eye catching devices, you get to stick the straights on. Check your tire pressure, tire condition, light functionality, and also perform a quick overall visual inspection at every startup, heck you could slap on the shorties. After all, at that point you actually do care about your safety (and probably wouldn't want to cheat your ears either).
Usually the louder bikes I notice share four things in common. Tee shirt, jeans, boots, and sunglasses. Definitely safety measures, not trying to impress onlookers...