As you may or may not have noticed, only a few companies have fansites for their entire company. I guess that is because those companies are awesome and have a united community. Yet most companies have fansites only for individual games or franchises. A few (if not all) exceptions to the rule are below:
Blizzard Entertainment - Nearly all (if not all) fansites (SS Free, WarBoards, ORG Network, The Nexus, BlizzForums, Planet Mac, Trollz, BattleForums, BlizzCraft, GhostCraft, StealthBot, SubBot, etc.) support all three major Blizzard franchises (plus, some even support Blizzard's cancelled games).
Reenactor Entertainment - Nearly all (if not all) fansites (SS Free, Explosmertacular, Planet Mac, Trollz, etc.) support all Reenactor products.
Runic Games - This company has three fansites (SS Free, Runic Games Fansite, Runic Insider) that support the entire company.
Relic Entertainment - This company has atleast two fansites (Relic Rank, Relic News) that support the entire company.
Flagship Studios - This company has atleast four fansites (SS Free, FlagshipStudios.org, Flagship Forums, Flagship Wiki) that support the entire company.
Hatton Vending - This company has atleast one fansite (SS Free).
But most companies don't for example, you don't see any "Activision" fansites, or "Electronic Arts" fansites, or other companies that released 5000 horrible games that suck ass each year. This may be because they release a bunch of shit games that no one cares about (excluding a few games out of the status quo of 5000 year that are actually good, or are atleast partially enjoyable).