From what I understand, Martin doesn't radius their tops either but most kit builders do to counter any flaws in their workmanship.
FWIW, putting a radius on a top or back (which often have a 16 foot radius) doesn't have to be hard or expensive and I liked to make my own jigs in order to understand the process. I bought a pair of
these from Stew Mac and planed/sanded the appropriate arc on the underside of the X braces and lower tone bars only and glued them on using clamps and cauls. I didn't even make use of a radius dish.
BTW, I didn't radius the underside of the "#1" upper transverse brace; I kept it flat because the fingerboard lays atop it and that area actually needs to be relatively flat in order to better set the neck angle IMO. Again, I made my own gobar deck/work table but here I used a flat surface underneath, not a radius dish as is the practice. Note the LMI jig sitting on my vice to the left.
I also used the jig to transfer the radius to the gluing face of the kerferd lining on the sides. I did this by removing the plywood caul from to plastic handle and tracing the arch on the side of a 2x4, extending it to a length of 24" to span the length of the body of the guitar and then using my jigsaw to cut out my own larger caul. It was my economical DIY alternative to spending $160+ on 2 radius dishes and sanding paper. The operation of my jig was for the rims was similar but required some hardware to keep the caul at a uniform height:
