This makes all kinds of sense to me-- think about it, how did people deal with babies' elimination before diapers were invented? The babies were not just going all over the house (or hut, or cave, or tent, etc.). In the U.S., most people first train their babies to go in diapers, then they have to teach them later that what they've been doing their whole young lives is wrong, and now the kids have to learn to use the toilet. It seems to me like it's much easier to just train them not to pee and poop on themselves right from the start, while it's still instinctual.
Granted, it seems like it's an easier path if you have the luxury of staying home with your baby without returning to work in the first year or two. But if you choose to put your baby in daycare, this book does have encouraging examples of ways to train your baby "part-time" in that case-- you're still in charge of your baby all night, after all. There are lots of helpful photos of different positions to hold your baby while they go, and descriptions of various methods different parents have used successfully.
The book doesn't promote one silver bullet, some magical technique that will enable every parent to help every child develop perfect bathroom hygiene. It's more of an encouraging guidebook to give parents different tips and tools to use as they determine what exactly will work for them and their own baby. Every situation is going to be a little bit different, based on the temperaments of the baby, the parents, other caretakers, and the community. But regardless of the situation, there is never a reason that diapers must be used exclusively.
UPDATE: My baby is 8 months old now, and was pretty much trained for #2 by the time he started solid foods at 5 mos. So we changed dirty diapers for 5 months, since then it's been just wet ones with an occasional dirty one now and then when we weren't paying attention. And he's just now starting to actually sign with his hands (we taught him to make a fist and wave it around by his head when he needs to go) when he needs to use the potty, so it's getting really easy for us to catch more of the #1s also. If he keeps up at this pace, he'll be in training pants soon, hopefully out of diapers completely by the time he's a year old. While we couldn't manage being literally "diaper free" , we certainly use fewer diapers than most since the baby keeps them clean by waiting to use the toilet instead of the diaper.