Both games employ various strategies to keep gamers online and provide incentives to encourage their friends to join, for obvious commercial reasons. However, these incentives also encourage new, online friendships, particularly in Stormfall, creating one of the great pleasures of the games: a co-operative, collaborative effort.
In Farmville, this is made really explicit, as the game prompts players to 'share' and 'help' each other, but in Stormfall the practices of the 'League' I am involved with are very similar. The League's 'code' is in fact even selfless compared with Farmville, as while farmers are directly encouraged to share and help their friends, it is always done to obtain a similar 'gift'. Members of the League speak of each other as 'family' (although most have never met offline) and freely donate items to assist one another without necessarily expecting anything in return. Members also defend each other's castles when enemies attack, and help capture and defend neutral settlements that provide resources, which is a little different from farming... but the principle is the same.
Another key pleasure of these games, at least for me, is the acquisition of stuff. Cool stuff like dragons and golden chickens, that it takes time and effort to achieve. There seems to be a capitalist drive and pleasure here that I might expand on at a later date, even leaving the issue of literal commercial transactions aside.
Still - having three dragons is just awesome.