I don't think they do. Print journalists compete directly with the 6am/12pm/5pm/10pm news on radio and TV in that they're providing exactly the same material.
An author isn't competing directly with Radio, TV or Cinema, in fact the three are generally seen as complimentary markets. I've barely seen a good/great movie in the past decade that hasn't come from a book. From these films made from books, they explode the sales of the books.
Movies and TV is never going to replace literature, the cost->outcome ratio is far too big for movies than it is for books. I'm a writer, I'm currently working on a novel and I only have to do a couple of hours a night to be doing 1,000 words a day. Supposing I'm hitting only 250 words an hour (about 1/2 of what I usually do and I'm by far from the ideal writing situation that I used to have when I was working as a reviewer; this would easily factor in editing and other work for sale) it would take about 320 hours to write a novel length book would cost me as an author about 3300 dollars (as I'm unlikely to get paid any more than ontario minimum wage if I get a second job), which would more likely be 2500 after taxes.
That's 2500 dollars for a book you could publish. Worst case, self-pub an eBook on Lulu at $0.99 with their 50% royalty rate and you'll only have to sell to 5,000 people to break even. If you actually sold the book, you're likely to see between $2,500 to $5,000 for a first-time advance at a genre imprint, which means break-even or profit from the get go.
Break even for a movie is in the millions of dollars. Survivability for most TV shows is in the millions of viewers.
There's such naivety, yes traditional publishing sales have diminished and hasn't been immediately translated into eBook sales of the same figures (no shit sherlock the books cost a lot less, meaning there'll actually be market for more books for the same dollar value). In the 1940's 60% of the US population went to the cinema weekly. Since the late 1960's it has been steady at 10%. IIRC Nielson reported a 6% decline in TV viewership between 18-34's during the 2010 summer months.
Markets change, which is a fact of the free economy. The written word isn't going to die off because the paperback declines. Video isn't going to die off just because we stop going to the cinema or watching TV.
Just look at webcomics and the dozens of artists who are self-sufficient because of it. Look at Mike and Jerry of Penny Arcade, they employ eight people besides themselves because of a webcomic and this is before the traditional medium (comic books) are seeing the kind of declines that newspaper comics are.