There is a very simple reason why the argument of this book fails. Hawking does not address the pure logic of how something can emerge from the property of nothing. Something emerging from nothing is a logically contradictory idea. It CANNOT be true, because it is logically impossible for nothing to produce something. The two properties are opposites, and are therefore logically incompatible and irreconcilable.
If you examine the concept of something emerging from nothing as a pure concept, completely separate from anything else, it is clear that nothingness CANNOT produce something, in and of itself. Using only the concepts of "something" and "nothing," this idea is completely unworkable. In order to explain how something can be produced by nothing, you will have to tackle the logical impossibility of something emerging from nothing. There is no rational progress that can be made in this area, to my knowledge.
Hawking claims that the property of gravity causes matter to just appear out of nothing. When certain conditions are met, matter just appears. And that's as far as he gets into the subject. He doesn't explain HOW matter is produced from nothing. He simply claims that this is what happens under certain conditions, and that's it.
This is very, very different from explaining the actual logic of how something can come from nothing at all.
And therefore when Hawking claims that the Universe needed no creator, he has no grounds whatsoever to make this claim. Logically, something can only come from something else. And so it follows rationally that the Universe HAD to have come from something else, some other cause: a creator, a God, or SOME thing. ANYTHING would satisfy the equation better than nothing.
Hawking is going beyond the bounds of what he can legitimately say as a scientist. As far as science can determine, the universe came into existence from nothing. Hawking has no grounds for going beyond this understanding into the realm of metaphysics. He is not explaining anything here at all. He is simply stating his opinion.