In the MMO genre I believe developers should focus on building worlds, not just games. The more developers do to create engaging settings that players grow to care about and become invested in the more enriching the experience it will be for the players. This in turn will make it more financially rewarding for the developers. Loyal customers, especially in an increasingly microtransaction dominated economy, help keep games a float.
Read more of Rob Lashley's Connecting Players to Virtual Worlds.