Found in the Macrumors forums:
[Analogy of the movie inustry vs Apple Rumor Sites] BUT...they do NOT go after rumor sites like AICN because it ONLY alienates fans and pisses people off. Plus, you’d spend your entire time filing lawsuits instead of making movies if you went after every rumor site out there.
But ... rumors concerning movies often encourage people to buy merchandise and to go to the movie. Movies are also previewed for critics ... Apple products are NOT previewed months in advance for critics. (At least ... not for critics/beta testers to publish "reviews") Rumors about Macs often discourage or delay purchases.