DR3 is great but its not really universally or dude-bro appealing so it cant have been much of a "system seller" on its own even during the launch drought. Beyond that, the vast majority of any particular game's sales come in the first few weeks of release. I actually saw some data sheets on this from a buddy who's a regional mgr for GamesStop and it amazed me how sharply game sales drop off after just a month. Even the biggest hits slow to a crawl within 90 days. So, they really have not much to lose and a lot to gain by releasing on PC.
What? No. That's a complete lie.
It had a bug which didn't recognize wireless controllers, and I'm not sure if they ever fixed it, but the game absolutely had controller support from the start, generally speaking.
I could see MS putting the Gears and Halo collection on PC to drum up interest. Though then again, they need all the help they can get, so maybe a few months after they release on X1