I guess I don't agree it is a silly rule. I always use a 75 for piecing. It leaves a smaller hole and works quite well with the thread I use for piecing. For quilting on my domestic machine I generally use a 90. It is more robust for handling the multiple layers and the thread I use for quilting.
BTW: I have used a needle as small as 70 for sewing batiste with a 50 weight thread, and I would have used a 65 if I'd had it. I also have used a 100 needle for heavy jeans and topstitching thread. Using the right needle for the right task is just a reasonable thing to do.
Pam