I've blogged about this. What most of these commentaries seem to miss is that the material cost of the AppleTV is only going to drop since the hardware requirements aren't going to change much.
Look at the bill of materials. There are $100 tied up in CPU, Chipset GPU & network chip. How much will that cost in 18 months?
"The iPod makes money. The iTunes Music Store doesn't," http://news.com.com/Will+iTunes+make+Apple+shine/2100-1041_3-5092559.html
Of course that was a few years ago... maybe things have changed...