I tried to post a new topic to "Validated News" forum but I'm greeted with the following error:

"Sorry, you do not have permission to start a topic in this forum"

The forum description states that:

"Discuss current news items. Developers can start a news thread here directly."

What's wrong? Have I misunderstood something?

The forum description is wrong. Post to News Submissions, us mods will handle the rest.

Ok. I already posted to that forum yesterday. Thanks.

Fixed the description. It used to be so that they could post directly IIRC, but then we figured out that the developer of something itself isn't the best judge whether news is of interest to the general HA population.

People should be allowed to edit posts in the news submissions forum without a time limit. There's a post in there right now that would be worthy of validation but currently has no abstract. Hopefully an exception has already been made for this forum.

No, because IPB doesn't seem to allow that. I just hacked up the source and now it hopefully works as you requested.