How far back should your knowledge go?

How can an article about actors playing made-up versions of themselves not mention Being John Malkovich? The omission is almost as egregious as the one FT video game writer did to Planescape: Torment. Both of the snubbed works of art came out in 1999, which I can only assume was too far behind the authors’ time horizon, but then if you write about a field for a living shouldn’t you know about its (fairly recent) history? I am of firm believe that to know a thing is to know its roots. Yes, this can go too far — see the name of this very blog — but most people most of the time don’t go far enough back, the most common knowledge border being their birth year. Which is fine for a blogger, not so great for professional journalists.