I think these people are deluding themselves. Sure, dogs may cost a little less than kids in money, but not in time. Dogs severely hamper your lifestyle unless you work at home and don't leave the house much. Kids hamper your lifestyle for about 2 years, and then it eases up as they become more independent, but dogs never get to that point. Worse, there's a lot of things you frequently can't do at all with a dog, that you can with a kid, such as going shopping, going on a foreign vacation, etc.