For those curious: The BOOK ending spoilers!

Yes, the bit with the lie detector on the answering machine was in the book as well. It definitely was a turning point for Kat as we saw, where she realized that her father was actually capable of keeping things from her.
I can see the parallels with the homosexual attitudes during the 80s as well. After some thought, I kinda preferred the movie ending a bit more (sorry for the mini rant ;___:):
The film and novel are told from the perspective of the unreliable perspective of Kat. Everything she sees, or witnesses, may not be as it had actually occurred, mostly with her sexual awakening of sorts. She's a teenage girl, everything that is going on with her life, outside of her home life, is what is genuinely the whole world to her, and what matters the most. Also that she has finally understood the power that her body has on people. In this sense, this really reminded me of American Beauty, as well as the attitudes of suburban life, and the deconstruction of it.
Now, everyone was quick to assume in both the film and the novel that Eve had run away, and was obviously having an affair, because she wasn't satisfied with her marriage, and everyone was quick to feel sorry for her father, being how innocent and perfect he seemed. And as we learned, nothing is as it seems. I suppose the secret to Brock could also explain himself distancing himself from his wife sexually, as well as Eve reading all those books, and trying to satisfy him, even though she never could in that manner. As well as THAT laugh that Eve does, a laugh that combines not only the shock, but the realization and explanation for her husbands mannerisms, and participation in their marriage.
In many ways, Kat had the same idea of Phil as her father, she mentions he's kinda dumb, and really has no motivation. Now while that may be, of course he himself was possibly looking for escape from his mundane life in other ways? Not sure really. I feel that Phil's part in having an affair with either the mother or the father ultimately ended up the same, but I feel where the movie ending might have come to mind in the writing process was when Phil tells Kat something along the lines of "Ask your father, he's got your mother under his sleeve." Which I guess could be interpreted in different ways.
Once Kat realized the truth of what had actually been done, the image of her mother she had numbed herself of after all these years had changed in that instant.
I suppose going for the book ending might have been cliche in film form? We could never know.
Regardless of what you think, many are saying that it being a film by Gregg Araki and him going for shock value, which he does in his films (which I tend to enjoy), or if you enjoyed the film on its own, I think ultimately both endings work well in their respected mediums.

>>The ending was changed for various reasons, the most obvious because since females will be the primary target audience>> That way, 80% of the audience can go home thinking "those damn men!!"

It's more about the director's existential viewpoint:

But being gay in a society like this totally affects my films. Being gay, or queer, as the lingo goes, does put you outside or underground.

Although Eve didnt have sex with Phill she was far from being a perfect woman, and it's not like she was loyal to her husband,it was obvious she actually wanted to sleep with Phill

Yeah, because _just_ killing her isn't making him a horrible human being at all... Come on.