Hey jno: I'll list your points as you did (I don't know how to italicise with the new site... so can't quote like I normally like to).
1. Editing/selection: I think for this point you've assumed that newspapers or their online equivalents will die out completely, which is the only real scenario in which your concern might happen, and even to begin with that assumption is flawed, but let's go with it for the sake of argument. Granted, there's no real way I can guarantee this, but I'm willing to bet that at the very least some kind of online replacement/replacements will spring up. There'd be a huge 'gap in the market', wouldn't there? And take the success of some journalistic sites that are far more exclusive/sectional in their coverage - like The Escapist, for instance, which covers gaming news, or Salon.com. I can't believe someone wouldn't be able to do something similar for something with a far greater target audience like current affairs/news.
2. Authenticity. I think it depends what you're comparing on the web and with what you're comparing it to on this point. If you compare the authenticity of facts presented in the Times or The Economist against Wikipedia, it's obvious who comes out better. But I'd easily trust Wiki over, say, the Sun, or even some of the heavily contrived "facts" Littlejohn comes out with. British journalists can be just as unreliable as the internet. But with the internet, you don't just get access to exclusively web-based content. If something looks fishy you can easily click onto the site of a research institution you trust and see what they have to say about something. Or check the references, or choose to disbelieve it if it has none.
3. Professionalism. The issue you raise here is essentially about trusting the author of what you read. But you can check the the trustworthiness of a political blog in exactly the same way you can check the trustworthiness of a newspaper article: