I don't know all of the manufacturers' design goals, but I would wager a guess at the main ones: Aerodynamics, visibility, & weight. A car is not designed around a windshield. A windshield fills a hole in the front of the car where the driver needs to see.
You are correct, windshields are harder to break from the outside, but that's because of the inherent strength in the way the glass is shaped. A CONVEX side (the outside) of an object (windshield) will be stronger than the CONCAVE side (inside) of that same object.
Is that a design consideration? Could be. But I'm thinking that aerodynamics are to be credited.
As far as being ejected and getting killed: have you seen Red Asphalt (or any driver's ed. video? The "collar effect": when only your head goes through the windshield during an impact and then the body rebounds, sometimes decapitating the head). Hell, I think there was even an episode of CSI where this happened.
My GUESS is that there are 3 reasons the front windshield is made of laminated glass and not tempered glass: COST, SAFETY, & POST-BREAKAGE VISIBILITY.
Think about this for a second: The majority of manufacturers no longer include a cigarette lighter in vehicles. But you can add a Smoker's Package for a small fee. Where else are they trying to save money and maximize profits?
All of my information about glass comes from the 3 years I spent working in and learning about the glass business; from raw materials to fabrication to installation. I don't know where you're getting your information.
If you want to know a little more about glass, read below:
Glass must be shaped before it is tempered (if it is to be tempered). Flat glass is susceptible to breakage during this process, and curved glass even more so. Glass becomes SLIGHTLY obscured during the tempering process. To ensure that only the best/clearest pieces were used would mean a lot of pieces get thrown away (this drives up cost).
In the event the glass breaks, it stays in place.
If tempered glass were used, a breakage would cause the entire unit to shatter. You can't see to well through shattered glass, so tempered glass is not an option for this reason.
Tempered glass is not DESIGNED to shatter. It's just something that happens as a by-product of the tempering process and happens to be useful for automotive applications so you don't get shards of glass flying everywhere in the even it breaks. This gets into molecular geometry and a bunch of other crap I haven't studied in ages.
Can we focus now?