If you take the time of the announcement (in seconds elapsed since midnight, March 14th 1993), divided by the amount of letters in the FAQ, and then find the square root of the resulting number, you get 3!
Seriously though, are you suggesting that HL3 will only be released (even for a short while) the SteamOS? I agree it's possible, but I think that would piss all kinds of people off due to it obviously being a marketing ploy.
I would imagine a more likely option for them are discounts for various games on the platform for a few weeks.
Or the original Halo on the first Xbox. If I remember correctly that game alone promoted the console for a lot of customers. Valve could give HL3 a head start of a couple of months on SteamOS and release it on other platforms after that. It would be less annoying that being fully exclusive. Besides, all the PC gamers could just go and dual boot SteamOS on they PC. It's free after all.
