Rather than selectively hiding elements from print media,
That's the correct way of doing it.
According to whom? I've yet to see this as a W3C recommendation; in fact, this is the reason content selectors were created in the first place.
why not generate these using content: selectors?
Because then they won't show up when people print the page with a less conforming browser.
Consider the number of people printing Wikipedia articles from "less comforming browsers" vs. the number of people actually viewing Wikipedia articles online. Is this the correct assumption to make? Why do we have to endure such frivolities as painting the current URL boldly across the page, especially when this is almost always in the print header to begin with?
Timwi