This is my understanding about the roll bar, someone with more track day experience then I might be able to fill this in better. There is a difference between roll bars, and a roll cage. All Boxster's have roll bars; they are required by law in production convertibles. I believe you only need roll cages in PCA events when your skill and experience progress (there are different levels) or you are taking part in PCA racing. PCA racing is totally different the PCA drivers ed events.
STL PCA has two DE events a year, one in the spring and one in the fall. Read our application for the spring DE event, it might answer some questions.
http://vista.pca.org//stl/events/2005/April05CCRegistform.pdf