1) Mark Pombo's crash was so high speed that in a production based race car, injuries were almost guaranteed.
2) Triangular door bars do not allow impact energy to be dispersed slowly. Triangles are inherently rigid and as such, all the energy from a crash immediately transfers to the car. Notice how the Audi crash at LeMans (where the car was flew into a million pieces) let the driver walk away? Energy dispersion.
3) The NASCAR style door bars are not flat. The bars stick out to the side of the car a little farther as they get higher (or lower, I don't remember). Like the pic below if viewed from the back of the car (periods are roll bar diameters and the underscores are just for spacing)
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This way, the outermost bar absorbs some energy, then the next outermost and so on. This takes time and as such allows energy to be transferred to the car slowly, thus protecting the driver.
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