Kotaku reports on an interesting non-MMORPG incentive issue with this year's editon of MLB: The Show. The game will have six historic stadiums that can be unlocked in one of two ways:
1. Pre-order the game from participating retailers
2. Complete every one of the game's "trophy" achievements, a task that Kotaku describes as something that "takes a LOT of doing".
My guess is that the team was told to think of something they could hold back from the base game as a pre-order "exclusive", and decided that the platinum trophy reward was a good choice. Players who are dedicated enough to complete the trophy are seriously committed to the game, and will probably do so regardless of any extra incentive. Meanwhile, many players would not even bother trying for the trophy due to its high requirements, and therefore would not have done so even for extra ballparks.
Finally, and most to the point, it's a non-subscription console game. The developers don't really have a reason to care if players finish the top trophy or not, as they won't be paid any more if the pursuit makes the game last an extra month. In fact, one could argue that the developers are better off NOT encouraging players who don't want to finish the trophy to try it anyway. The devs will be looking to sell an updated copy of the game next year, and don't want to have customers get sick of it. As with Blizzard's infamous holiday meta-achievement, any such effort is bound to push players in the direction of some aspect of the game that they weren't playing because they frankly don't enjoy it.
More broadly, there's an interesting question here about the point of having rewards for 100% completion of a game in the first place. In some ways, historic ballparks fit that particular bill nicely, since they're cosmetic additions that might perhaps liven up the game slightly for players who have already seen it all. There wouldn't be much point in having a reward that has an in-game function, since the game, unlike a persistent world MMORPG, won't carry over into next year's edition. Then again, bragging rights are still good for something, or would have been if they weren't up for grabs with every pre-order. Perhaps something more visible, like throw-back uniforms that could be used in online play, would have been a better choice of status symbol in this particular game.