It's waaaay more profitable to sell the same device for three years without updates: it costs nothing in r&d. This wholy explains the mind boggling profit margins doesn't it?
It's weird- the practice of never talking about product roadmaps started in an era when whatever customer angst and uncertainty it generated was vastly outweighed by customer and media delight when the next step in that roadmap was finally revealed, which at the time happened like clockwork at 6-month intervals. Now people want them to talk about product roadmaps not because they're excited to know when/what the next great Mac is going to be, but because they're worried that there won't BE any Macs anymore (at least not any that they would want to buy). :(