The standard page is mounted onto thin black backing.  The result is a slightly thicker page.

When the album is closed, the page edges appear to have a black and white "striped" effect.

The thin page is mounted directly to white backing core.  The result is a more modern look

When closed, the page edges are all uniform. 

Thin vs. Standard Pages

Here you can see the difference between the page types.  The thin is on the left, the standard on the right.