Well, once you get down to 318 bytes vs. 212 bytes, the server overhead alone is probably more than the filesize. It generally runs 597, 598 in my logs.
Most visitors ask for the precomposed apple-touch-icon first, and then they may or may not go on to ask for the vanilla version. So either I've got atypical visitors a possibility I can't exclude or the touch-icon documentation page is misleading. Hardly anyone asks for the 144x144, which is what they tell you to have if you don't carry all sizes, and they make it sound as if "precomposed" is second choice.