Users email us to complain when they see posts that break this, because "Show HN" is an implicit contract that they'll be able to try a piece of software out. (The standards are looser for non-software projects.)
There are three things at the top of page that are brand new and people can try out (plus we sent almost 100 copies of the iOS app so far to people who signed up this morning):
* https://chrome.google.com/webstore/detail/nneejgmhfoecfeoffa...
* https://addons.opera.com/en/extensions/details/adblock-fast/
The logs turned out to be more complicated than I thought. You submitted "Show HN: A preview of our iOS 9 ad blocker". That did break the rules—a "preview" can't be a Show HN when the "preview" is an email signup and an image. A moderator changed that to "Adblock Fast", and then a moderator changed it to "Show HN: Adblock Fast – An iOS 9 ad blocker".
Since you do have new things for people to try out, though, it seems like making the title more general is the best solution.