I don't see it as so many kids here having sleep problems, but more showing the broad range of what is sleep in the age group
Actually you are quite right. Most parents aren't told that it's normal for babies and toddlers to wake in the night until they are 3 or 4 years old.

DS1 slept 12hrs most nights, but not more than 20 min during the day. DD woke every 3 hours every night until she was 3 or so. DS2 does something in the middle- sleeping well some nights, waking all night others.

Currently I'm studying paediatric and community nursing and the fact that young children have so many development changes in their first 3 years that can disturb their sleep.
While I know this may not be comforting at the moment it does mean for the majority of kids their sleep patterns settle down after 3 or 4 years old. It doesn't last for ever