K.,
There really isn't a clear cut answer to the whose right question? The answer is going to depend on your beliefs as a parent.
I have several friends with little ones who started sleeping through the night very early on. Their parenting philosophies tend to be more parent centered and more schedule centered.
We are a more child centered family. We follow many of the Attachment Parenting Principles. The idea of a "fourth trimester" and adjustment period following birth make sense to me. Also, we are a breastfeeding family and DD was nursed exclusively to 6 months, so especially early on, she woke a LOT to eat around the clock - and that's normal.
I had a great stretch of sleep from 3 months to 6 months. At 6 months, she went from sleeping a 4 hour stretch and a 6 hour stretch at night to waking every 1.5-2 hours at night. From all my reading and research, I felt most comfortable with the philosophies that said that the absolute earliest children are capable of sleeping through the night is around 12-18 months. We had a few travel conflicts that stopped me from starting to sleep train until about 15 months. At that point though, she was totally ready for it the process was super simple and fast.
Good luck to you and your family in figuring out what works for you.
S.