Illegal or unethical?
As a thought experiment:
Couldn't you turn it around and say it's unethical for Apple to allow customers to buy phones knowing full-well that they are going to introduce a top-of-the-line model in a few months?
Isn't it in Gizmodo's best interest (as a journalistic establishment that serves the best interests of the people - again, just a thought experiment) to let people know about this?
How is it different from DaringFireball talking about an Apple tablet device based on inside information that he received?