I suppose it would depend on sales and what one can get one compared to a regular ZR2, and what folks place on the value of the add ons - particularly factory installed and warrantied items such as the skid plating, winch ready front bumper and rear bumper. I usually go aftermarket with wheels as an example, and I quite dislike the factory regular ZR2 'cock-n-balls' wheels, while I really like the ones on the Bison. That has saved me a bundle, as I'm not out shopping Methods or the like.
The AEV front bumper isn't ideal in a few respects, but neither are a lot of aftermarket stuff that will hang down just as far or offer up other challenges like added weight, bulk, etc.
For the most part, I think a lot of the AEV stuff for the Bison (both factory equipped and the AEV aftermarket) is compatible with the ZR2 and lots of folks have added AEV stuff to their ZR2s, but buying the stuff piece-meal isn't cheap, and certainly not cheaper than getting it equipped at the factory.