My blog, which frankly shouldn't be a blog, has one post on the front page that people come to see. If I update this post and ping google, does G count that as me adding content to the blog and reward me as it does others? What if I add a page but don't add posts? Does this count as "adding fresh content?"
When you update the post on the front page, Google does know that your site was updated and that does help. As to whether it counts as adding content, it depends on how you change the post. If you are adding stuff, then yes, its content. If you are deleting lines, then you aren't adding content, but are updating the site still. Adding new pages does count as adding fresh content so long as the pages have new, unique content on them.
Absolutely, maintaining a blog is the best way to keep your content fresh and it is very easy to add new content
I guess google will not count it as a new content since your url did not change. Google will just see it as an updated content.
If you think that by adding few keywords in old article will make it fresh content than you are wrong . Google bots first and mainly go with post url and tittle keywords and if they are already indexed than you will not get any help . So by updating that post again and again you can't make it fresh content .