Sony gave sister site Kotaku Japan a list of games that require memory cards for saves and a list of games that do not. So who decides which games need memory cards and which ones don't?
According to Sony Computer Entertainment, the game companies do. Kotaku Japan is reporting that it is up to the game makers to decide whether they want to have data saved on the game card or require a memory card.
What's the difference? Games that use memory cards can support post-release content such as DLC and updates.
Kotaku Japan was told that it is not possible to save game data on memory cards for games that were designed to save game data on the actual cards. This all apparently means that games that do not use memory cards won't get DLC and cannot save data on memory cards. See the update below.
Stew on that. What's looking to be a great portable could be hindered by save formats, and then later resurrected by an inevitable hardware revision.
Update: It sounds like card games can support some sort of DLC. According to Sony's Vita FAQ, the game card "can store add-on game content or the game save directly on the card." That sounds like DLC is possible for game card-only titles. However, it's not yet known how large the downloadable content will be and what kind of size restrictions there will be.
とりあえずメモリーカードは買っとけ！ [Kotaku Japan]