Http://blogsearch.google.com/ping

[MargaritaS]

Is there any reason why a website would submit all their content (videos, photo galleries, articles) to this?

[KaneJamison]

You can submit your blog url or each RSS feed you have one time. That's sufficient, though it's not necessary to get added.

They're looking for content in a blog format, so any videos or photos contained within the post will automatically be found. Regular site pages wouldn't be appropriate to submit.