Why do perfume inserts in magazines count as two pages (and other times they don't)?

Question

I've recently noticed that the perfume inserts that are placed inside magazines will sometimes count as two pages and other times they will not. As an example, I'm reading the April issue of Glamour and the first perfume ad that I tore out counted as two pages (after I tore the ad out, the pages on the left side went from page 92 to 96, indicating that the insert counted as pages 93-94). On the other side, another perfume ad that I tore out in the same magazine did not count as two pages; the ad was next to a numbered page (186) and when I counted the page numbers until I got to the next numbered page (193), all the numbers were accounted for (186-87, 188-89, 190-91, 192-93), I concluded that the ad did not count as two pages. Is there a reason why magazines do that?

Answer 1

No offense,

but it matters?!

Answer 2

It depends on the magazines.