The key concept is called code re-use. If a game is assembled from core blocks the shared blocks can be reused when an Internet user switches between games. It's sort of like being Spiderman for Halloween one year and Superman the next: you can reuse the blue tights and red boots and have to pop out to Wal-Mart only for a cape.
- from PO Bronson's book The Nudist on the Late Shift