The world's natural wonders differ from the other grouping of wonders in that they were not made or improved upon by humans. They actually humble humanity.
The local native peoples have known these wonders for millenia, however this list came to the notice of the Western world relatively recently. For example, Mount Everest wasn't identified as the world's highest peak until 1852, and its exact height is periodically disputed to this day.
Today, these wonders have become places of pilgrimage, where awe is its own reward.