Interestingly, Cavalier 2.2 heads seem to show bolt holes, and perhaps studs and nuts are either a novelty or only applicable to certain years and models, or else there is an option whether to use studs and nuts or bolts.
From the photos, it looks as though all the bolts in a given row should be the same length of shaft (before the thread starts).
At the same time, the back row up inside looks slightly higher than the front row.
This would suggest the back bolts are longer than the front ones.
Another explanation for the difference in torque would be that the back row is doing the main job of holding the head on,
against the explosive force of the pistons, while the front row is more offset (not directly above the pistons).
This might be an alternate explanation for the back row (longer) needing higher torque.
In the pictures in my Haynes manual, the front row does however look like studs and nuts, as the other poster commented.
Now I will have to check my engine to find out what is on mine.