I don't know whether or not this is possible, but could only guess that SK doesn't have update news for patches (even major ones) nor events posted in Steam news for some reason? (I've noticed that the other F2P games on Steam don't seem to post news there either. Perhaps because we don't receive update data through the Steam client?)
I could only think that it would be a huge boost in the volume of players who would be made aware of SK, and how active the development of it is if it got News posts in the Steam News pane.
Not only would it be nice for us Steam players to be able to see what's going on with SK updates/events from there, but I know I've personally been intrigued enough to check out (and purchase) a few games from seeing them come up on there and impress me with frequently or significantly updated content.
Is this something that could be done?
I think it's because SK does not update though steam (like you suspect)- F2P games that use the steam client to download and update games are the ones that get a news feed, such as the recent Super Monday Night Combat.
They got some steam news when the expansion pack was released, because it was new content to steam. The news feed for updates is probably so that players know why steam just started downloading something.
It would be cool if OOO was still allowed to release update notes on steam, though- it would draw a bit more attention, like you said. Nor would it be a bad or detrimental thing- It's getting the permission that would be tricky.