CART/F1/IRL drivers more prone to spinal fractures than Winston Cup/Sprint Car?

When the neck or spine is flexed, that compresses the disks between the
vertebrae. So when the disks are already compressed the shock absorbing
capacity of the spine can be reduced to the point where fractures of the
vertebrae are much more likely.
I haven't seen any formal medical studies comparing injury rates, but it
does seem that you don't hear about spinal fractures as often among
Winston Cup and Sprint Car drivers as you do Champ car. It would not
surprise me if the seating position of NASCAR and Sprint Car drivers
when they hit the outside wall does make them less prone to spinal
fractures than Indy car drivers.

There is some instance of spinal injuries in Sprint car racing, I personally know a guy who fractured three vertebrae in a mini sprint. The problem came when his seat broke over the seat support back rail and allowed his back to bend over it during a particularly violent flip. Brad Doty suffered a similar injury in an Outlaw. I don't recall any serious back injuries of late in CART/F1/IRL or even sports cars. Most of theirs come from lower extremity damage. NASCAR drivers suffer damage from the violent snapping about in a much larger car. They are not as securely pinned inside the car as other forms of racing. Mark Martin's crash early last year was not all that terrific a hit on TV, but it damaged his knee, broke his wrist and several ribs as well as slipping a disk in his back.

Shortanswer to Frankie : No.

Sadly, I can think of one recent instance of spinal injury to an Indy car driver. Sam Schmid.

In both Schmidt's & Lasier's accidents, neither driver was using a seat molded for them - the seats were for the regular driver of the respective cars, neither of whom were anywhere near the sizes of Schmidt & Lasier. Pretty stupid move by both the teams & drivers. IRL has now mandated that ALL drivers use custom seats. Damned lousy way to learn a common sence approach to personal safety. The word "amateur" comes to mind - meaning a lack of professional thought process.