Am I missing something?
It's just a question of time and labor. Percentage-wise it's a big increase, but for the typical theater it's probably less than $100 difference.
I think the ease of use and time savings are worth it, but YMMV. If saving money is top priority then I would go with the rolls.
Edit: One other thing with the batts.. I just picked up some R-19 and on the new JM batts they are pre-split so you can tear them lengthwise. Depending on how you tear you can get 3", 7", 8" 10" etc.. pretty cool.
This is 15"x32ft or 48.75 sq.ft for $9.98
This is 8x 15"x7.75' batts or 77.5sq.ft for $42.91
A tip for cutting the roll is to put a scrap piece of plywood under your cutting area, then use a wide level (or anything wide and flat) to push the roll down. This makes it a LOT easier to cut.