It's not ironic at all. From the article: "They all look like placeholder icons made by a developer who would be the first to admit that they’re not an artist."

I think Gruber would be the first to admit that he's not a designer but rather a writer. His business is one person, himself. In contrast, Apple has over a hundred thousand employees, including quite a few professional full-time designers. You would expect Apple to do vastly better at design than Gruber.

What's ironic is if Alan Dye is no better at design than John Gruber.