On the other hand... If I am writing an article, and I intersperse my arguments with a lot of irrelevant pictures (which I often do on my blog), and go off on irrelevant digressions (which I sometimes do on my blog), it seems fair game to comment on the fact that my writing style is obscuring or detracting from my subject.

Coming back to ads on a blog, if those ads are interfering with with article's ability to communicate its points, isn't that the same as if the author's own prose interfered with the article's ability to communicate its points?

So we have two things. One thing is using the article as a kind of excuse to have a general discussion about the subject. We go off on tangents and discuss things not in the article (like whether it is useful to attach motors directly to the wheels, something this particular crate motor was not designed for), and with respect to that discussion, the ads are irrelevant.

The other thing is discussing the article itself, including whether it makes reasonable points and how well it makes its points.