Replayability is actually an issue, I think. If a game become too replayable, people will be too busy playing to buy new games. I'm not sure Halo1 replayers would be more likely to buy Halo3 with recent Halo1 gaming than without. Wouldn't it be better to have them sitting around wanting some new game to play instead? This is also a concern for something like LBP. What if the user-created content keeps people amused with that one title for ages. That'll be less content being sold. The only games where you really want replayability, from a publisher POV, are subscription games and games with buckets of advertising (Soccer) especially with live advertising being updated so you can charge companies for it.
The first title that pops into my head is World of Warcraft. The popularity and replayability of that game means (in my mind) that Blizzard will "never" release a new game (i.e. a hell of a long time). But the game itself is different from their other hit genre, RTS. There's a split fanbase where the RTS is the only interest (Read: Starcraft 2
).
So I think the replayability issue you describe is generally a problem if the new game "fails to deliver" by comparison. If the next title sparks no interest, being vastly different, replayability of the older title shouldn't matter. For instance, if Warcraft III was not so replayable, it does not mean I'll pick up WoW because I have no interest in online RPGs.
And that's not just it - People do have different tastes and will pick up another title from a different company if it suits them. There's a replayability factor, but people also do want to try new things, and a sequel is a safe bet
if the sequel has that same pull but doing different things that the older title did - something "new".
For something like adding gamer points to Halo or Halo 2 for 360 Backward compatibility, it should have been implemented in slower months of the year so as not to try and interfere with the sales of other titles. Has Halo 2's online, itself, hindered sales of other titles? I don't know, but there has been nothing that can replace it except for a sequel. I would have to go back and see what were the popular titles on Live before it came out (2002-2004).
Apologies in advance if it all seems incoherent.
Someone had to do the work, test has to be involved, distribution has to be involved, billing has to be involved, support has to be involved.
There's a minimum cost to just releasing something.
This is especially true for these maps because they are being made by a new start-up and independent company; some of the folks who worked on Halo 2 multiplayer made it (it's not Wideload Games).