After digging through the rule the NHTSA adopted, there’s nothing in there that mandates side glazed windows. The rule covers ejection mitigation. The summary hits the major point:

The agency anticipates that manufacturers will meet the standard by modifying existing side impact air bag curtains, and possibly supplementing them with advanced glazing. The curtains will be made larger so that they cover more of the window opening, made more robust to remain inflated longer, and made to deploy in both side impacts and in rollovers. In addition, after deployment the curtains will be tethered near the base of the vehicle’s pillars or otherwise designed to keep the impactor within the boundaries established by the performance test. This final rule adopts a phase-in of the new requirements, starting September 1, 2013.

There’s a lot of discussion in there. The document is over 300 pages. Some of it covers how the side windows can be down or could become deformed from a roll-over. For testing procedures the windows have to be pre-cracked or removed.

The Federal Registrar calls out side glazed windows in 49 CFR 571.226:

S1. Purpose and Scope. This standard establishes requirements for ejection mitigation systems to reduce the likelihood of complete and partial ejections of vehicle occupants through side windows during rollovers or side impact events.

and in 49 CFR 571.226 S4.2.1.1:

S4.2.1.1 No vehicle shall use movable glazing as the sole means of meeting the displacement limit of S4.2.1.

I anticipate that mid to higher end vehicles will have side glazed windows. While lower end vehicles will not.

Apparently it was because people’s arms (or even heads?) would hang out of the broken window when a car is rolling over at highway speeds.