If it is repeated then it is harder to maintain. If you have worked on a big project you know that it is way harder you have to change things in a few dif. places instead of just one, and there will be much harder to maintain consistency accross your style.
Can you give a counter-example where repeating CSS improves maintainability ?
When you have a base style sheet (it can be a framework or a base style sheet for your main application and sections overwriting them or custom style sheets for some tenants of your application or whatever) that you want to customize?
Many component-based designs also prefer repeating styles for each component because of maintainability but I guess they wouldn't be counted in the article as they use generated root names.
My point is, not repeating styles should not be the target, but it may of course be the side-effect.
Can you give a counter-example where repeating CSS improves maintainability ?