I think it all comes down to the question „how much work should be involved in a PhD thesis?“ and also, „how well should it be done?“
According to the link Linguist gave above, the author of this book seems to conclude that we use too much time in revisions, to produce the perfect thesis, so if I quote from the link linguist gave:
„In the end, as Cahn points out, "no one will ask you whether your dissertation was passed with major or minor revisions. All that matters is that you have fulfilled every requirement for the degree."“
I don‘t agree with this. I think it is important to do a good job, and if I were to hire someone for a postdoctoral position, I would consider the one that does his (or her) job well, although it is important that the person knows when to stop and actually publish something.
Although I‘m a bit suspicious about this 12-18 months thing, I think that this could be an interesting book, might be some good suggestions there...