Zynga might file for IPO as early as Wednesday

I'm guessing you're a neophile (as most people on HN are): you tried casual games because there was some sort of novelty to them, then quit. Most people don't share this motivation; they find it hard to understand why, say, you would sell your perfectly-fine year-old phone to buy the newer one. This isn't how social games have managed to attract the userbase they currently hold.

Instead, people play casual games for the same reason they, e.g., smoke cigarettes: because their friends are doing it—so there's social proof that it's something interesting to try—but once you as an individual try it, you're hooked into a "fun loop" [http://www.eldergame.com/2011/06/world-vs-game-emergent-game...] of instant, small rewards, that invokes peer-pressure to rejoin whenever you try to leave (taking a smoke break at work with friends :: being sent an double-incentivized bale of hay.) This isn't really something that can "wear off" over time; rather, it becomes an increasingly strong bond as you begin to base parts of your life around it (smoking when you go out for a walk after dinner :: checking on your virtual pets on your break between classes.)

Parlor games had a "boom" but the Bicycle company still makes a profit every year. Pokemon is 15 years old and hasn't died out. Pundits called video games a "fad" back in the Pac-Man days, but they're more popular than ever.

I don't see any indication that social games will die out, any more than electronic mail will die out.