This last part is something only a few publishers and developers have done really well. For example, 2K Games managed what seemed almost impossible at the time, and bred a longstanding Bioshock 2 multiplayer community. Between offering assets for wikis, and porting the game out of pocket to Steamworks as Games for Windows Live began shutting down, 2K Games did good by their community.
They also repeatedly tried to do right by them in terms of DLC. When it seemed like Minerva's Den might not release, they gave out the Protector Trials for free on PC. When they found out they could port it over still, they did, and they kept the Trials DLC completely free regardless. They also gave Minerva's Den for free to anyone who had bought the original, Games for Windows Live version of the game. On top of that, they made all multiplayer DLC free for everyone, and decreased the grind in the progression system so members of the community could regain their ranks quickly in the new Steamworks version.
This is how you reward a loyal community. You don't treat them like EA did with Dead Space 2, where they never ported any of the DLC, and when it was found some was already on-disc, EA just quietly made a few items and armor sets unlocked for PC users. They never got the Severed DLC campaign (which reportedly never got past pre-Alpha on PC before being cancelled on that platform), nor did they get any of the multiplayer patches.
Publishers and developers both need to learn from these and other examples, and understand that you don't survive through game sales alone. You need that community who will stick it out years from now. Bioshock 2 is thriving and active on PC after five years. By contrast, no one is playing Dead Space 2 on PC anymore. Consider that fact.