The general idea behind public stations is to keep big conglomerations from buying off the media. The problem with donation run stations like PBS in the states, is that a big donor can buy off them off some too.
Why should they? There are a myriad of sources, and when you add the web into the mix, that number grows even more.
Well most people still watch TV, and you can't believe everything on the web. If the media is consolidated into just a few companies, there is fundamental threat to democracy.
An interesting example: from what I hear there has been almost no mention of the FCC changes in the US press. They've agreed to bury that story.
We simply don't see it due to rules enacted by the federal government.