Why should you care? Because you’re more likely to need the protection of a headrest than you are an airbag. Rear collisions are common. The above painfully boring, yet awesome, video from the folks at the IIHS shows a failed test of a 2007 Dodge Nitro seat. (Hey, we like crash test dummies, ok?) You can see that the head is not supported from behind, which would cause the dummy to sustain neck injuries and have to wear one of those embarrassing neck brace things to school the next day.
Also worth noting is that even “good” headrests won’t work if they’re not adjusted correctly. According to the IIHS, the headrest should be positioned up around the passengers ears. Tall passengers are especially vulnerable to these sorts of whiplash injuries, because their heads are often above the support if it is not designed well (Ahem, Dodge Ram) or adjusted incorrectly.