OK- here we go...
SFI did major testing a few years ago and found 4 points to be more dangerous that 3 point.
4-points attach in the middle of the lap belt so when you go from 60-0 in 3 nanoseconds the inertia of your shoulders pulls the center of the lap belt up and off your pelvis. The lap belt is now wrapped around your soft abdomen and tears you in half or rips all the internal organs to pieces and you bleed to death before the corner worker can even get to you.
3-point shoulder harnesses attach at the lap anchor so the lap stays in place.
Factory belts are designed to last a long time in the elements and protect you reasonably well.
Race belts are designed to protect you really well and last resonably long in th elements.
And yes there is also some lawyer and bean counter types in there but if you have ever seen someone walk away from a nasty crash unscathed you won't even consider 5 years and a day.
Here is one of my favorites...
http://www.youtube.com/watch?v=8h2iqmliVMk