I'm actually in a rental car about 80%+ as I travel for work and usually I'll use warm to very warm water to clear the ice as it's faster than scraping most of the time. Never broke a windshield doing that. I did, however, crack the windshield on a rental a few years back when I turned on the defroster. I'd left the defroster off until the car warmed up and within about 10 seconds of turning on the defroster the windshield cracked. I did not have a rock hit the car while I had it so it must have been damaged or stressed before I had it. National tried to force me to pay for it but my company, which does boatloads of business with National, convinced them to take a hike.
My previous car, a 2004 Toyota Matrix XR was traded in with 125,000 miles when I got the 2012 FF and the windshield on it, which was original, was so pitted and sandblasted it was sometimes difficult to see when driving into the Sun.
2012 FF Ti HB Sonic Blue, Built 5/7/12, 401A + Parking Technology Package and MFT w/NAV 3.0.2 -> 3.2.2 -> 3.5.1 -> 3.6.2