The trailer did not confirm the new ending.. the explosion is in the book as well, about halfway through. It's a dream sequence. And ODV, what do you mean why did they call themselves "Watchmen"? It's from a latin phrase which translates to "Who watches the watchmen?", "Who watches the watchers?", "Who will guard the guards?", "Who shall watch the watchers themselves?"
Overall, I think this is a much better trailer. To non-comic fans it gives a clear understanding of the plot, whereas the first trailer was pretty ambiguous. The music is also a nice touch. The first half is ominous, and it kicks in with Muse's "Take a Bow" in the second half. I like it.