Well, Rolex PR department didn't invite the blog to tour their factories just because they were feeling generous that week. However it's difficult to write about things that people want to buy without advertising them, in some sense of the word; and even more difficult if the things are just made by one company, as is often the case with collectibles. Similarly, an article on Jaguar cars would be no less interesting if Jaguar provided the author a tour of their assembly line, but if skillfully written, can still be journalism rather than pure advertising.