On the one hand, drivers have far more protection around them as a safety precaution. The problem with Junior is that he's been racing since the late 90s when that wasn't the case. He's taken his share of tough blows before NASCAR made leaps and bounds in driver protection, so it's possible that those early blows have made him more susceptible to concussions.
I wanted to bring up Franchitti but couldn't remember if the concussion was the deciding factor. Had to look that up and I'd say it was spinal injuries in conjunction with the concussion:
http://www.usatoday.com/story/sport...dent-head-injury-chip-ganassi-racing/3587919/
Wow. I had forgotten Junior had concussions back in 2013 as well. Can't say this current situation is looking good, tbh.