Personally, the value of DLC carries over the the value of the base game. Good patching with free additions makes the game itself better value, I'm more inclined to revisit a game I once skipped over (particularly when it gets a price cut; once the "complete edition" comes out the separate packages are irrelevant to me).
Similarly, paid-for DLC carries over. When reconsidering buying a game I consider it all as one package. Therefore when the DLC is good I'm more likely to buy the original game too.
But when the DLC costs money yet seems to be including stuff that maybe should have shipped with the game, or stuff that simply isn't good value, it devalues the original game too. Partly because it's a total cost : total value thing, but partly because I just assume they took the same attitude with the game.
Oh and level editors & mods. These mean developers have a community producing extra content for next to nothing. Every time they release a decent mod, the game becomes that bit more appealing to people who once skipped over it. Civ IV is a great example of this, some people buy that game just to play Fall from Heaven mod. Some people buy the game, keep playing it due to mods then buy expansions. Some publishers seem to be taking the approach of "monetizing" (I really hate the word) everything, and that a high value game does nothing but raise expectations and slow down the time until the next game is bought. For these people free content doesn't just cost to produce, they think it costs them sales of the next game too.
This comment was edited on Feb 21, 2009, 09:06.