Yeah, I think what it's trying to say is more like this: the blitter is what made it practical to move around enough image data with enough bit depth for the 40

Yeah, I think what it's trying to say is more like this: the blitter is what made it practical to move around enough image data with enough bit depth for the 4096 colors. For PCs without a blitter to get to comparable results took several more years of increases in CPU and memory speed.