The news that Halo 4would almost certainly not be coming to PC was a kick in the teeth to fans of the series, but now it looks like — just maybe — things may be set to change on the Halo/PC front in the future. Listings pulled from the Steam Database, which are almost universally accurate indicators of future plans, indicate that not only Halo 3 but also Halo 2 and the original Halo: Combat Evolved are on their way to Valve’s service. Also spotted in the database are listings for Fez, Duke Nukem 3D: Atomic Edition, Shadow Warrior Complete Edition, Dyad, Quantum Conundrum 2, The Witness and Second Life. Check out the full list of uncovered items over at NeoGAF.
Apparently they said they have "no plans" to port Halo 3. However, I heard 3 years ago from an inside source that they had one in the works for some time. That said, it's been three years and thus I am incredulous.