You may or may not have been aware of this, but there's been something of a minor exploit in Steam's platform that developers have been using to get their games to appear in premium spots on the Upcoming Releases list, but starting today, Valve have confirmed that they have now put a fix in place to stop this occuring.
The exploit centered around the developer API that publishers use to add their games to the store, and more specifically, set the release date. Publishers were able to change the release date in the back-end of the Steam platform freely, without changing the actual release date shown to customers. As such, they could keep setting a new date in the not-too-distant future in the Steam back-end, and as such, their games would appear in the top spots on the Upcoming Releases list on the store front page.
Valve have known about this skulduggery since March, but have now implemented a fix to the problem. Valve say that any developer now changing the release date will be presented with a warning asking them to contact Valve if they want to make any changes. As such, all developers or publishers will need to contact Steam to make a change to the release date of their games, and will no longer be able to do this themselves.
Publishers can still release games early at any time, but won't be able to change the scheduled release date themselves, assuming the game has been approved by Valve.
This will effectively put an end to the practice, and mean the upcoming releases section should actually contain, well, the next upcoming releases.