I don't want to single any one out, but the "some kids are just late talkers" is not necessarily a good thing to go around saying. Some kids have genuine speech problems, and it's not that they are "just late talkers." If my daughter had been "just a late talker", well, our lives would have been so much easier! Autistic kids often need pediatric speech therapy. Kids with lisps and other problems need it.
In my daughter's case, her inability to make herself understood was causing a naturally merry little kid to become silent and sad at age 3. Her pediatrician dismissed my concerns, but thankfully a preschool teacher I spoke to echoed them and helped me get my daughter tested. Putting her in intensive speech therapy (she had speech therapy three times a week that first year) saved her personality. The first time she was able to say her sister's name, I broke down and wept. It took years of hard work, but she became relatively normal in speech. (Incidentally she had some cognitive problems which vanished when she became able to communicate-- which turns out also to be normal. The brain cannot process some things without being able to use language, evidently. A child who appeared severely subnormal has now become a published author by age 11 and a charming, funny girl with a powerful mind).
My daughter had a disorder which meant that she had a very limited ability to control the movements of her tongue. Funnily enough she was an extremely picky eater, and it turns out that those things are linked. Speech therapy taught her how to move her tongue so she could produce the needed sounds for intelligible speech.
I know other families whose children have been greatly helped by pediatric speech therapy. Rather than telling people that "Oh, some kids are just late talkers", I think it is much more supportive and helpful to say, "I'm sure your child is going to be fine, but you can take them to be evaluated for speech therapy and that might give you peace of mind."
/sermon Sorry to preach, but as you can see, people being dismissive of speech problems -- even if their hearts are in the right place and they mean only to be reassuring -- hit a nerve with me. Now that pediatric speech therapy has become a developed profession, we can make kids' lives better. I note that the book "Late Talkers" was published in 1997-- and over the nearly 20 years since then, the field of pediatric speech therapy has evolved.