Yeah, there’s been nothing to suggest Valve have been working on L4D3, and while HL3 is out there somewhere I highly doubt they’d announce it alongside something like Steam Box.
This is very obviously a Steam Box (or whatever they decide to name it) announcement. My guess is the three separate sections on that page are all related, probably along the lines of:
- Steam Box hardware
- Dev tools for third-party Boxes
- Streaming service that works with Steam Box
I doubt there’ll be any new games announced. At best, maybe they’ll announce existing games that will be running on Steam Box.