Dedicated channel for news? or a channel for blog with a news category? A clean installation of Craft includes a 'News' channel which has confused me slightly. Would it not be better to have a 'Blog' channel with a 'News' category?

What is the advantage to having a dedicated 'News' channel?
Not every website has a 'blog' section. If your site's other content would, for instance, be something completely different like general company info, it would make perfect sense to have a news section.

In case you do have a blog, it would be perfectly possible to delete the 'news' section and give the blog section an entry type called 'news'. That way you would be able to give news entries their own fields, which is convenient.

It's all possible with Craft, so it really is up to you.