IKEA catalogue has 208M copies in circulation. Does that mean IKEA is The Truth? :-D
And I'm quite sure there are other free product advertisement periodicals that match Watchtower's circulation.
Watchtower isn't really a magazine; it's a sales pitch in a thin advertisement folder.
Imho the difference between a (real) magazine and an advertisements is this: in magazines, the articles are the product. People buy/read magazines because they enjoy the stories, interviews and whatnot.
In advertisements, there is a product or service being sold. The interviews and stories aren't in there for themselves, they are there to push a product or service.
Watchtower qualifies as advertisement to me.