Here's a suprising notion that might explain both familiarity and habituation in games: catchiness.
Think about a catchy song, the kind you can't get out of your head when you hear it. How does that happen? The reason songs stick with us is unclear, but some researchers have called it a "cognitive itch," a stimulus that creates a missing idea that our brains can't help but fill in. Whether the brain science is true or not isn't really important; it offers a helpful metaphor through which to pose another question: what causes the itch?
Paul Barsom, a Penn State professor of music composition, suggests several factors that seem to aid in making a song catchy. Conveniently, they correspond well to my re-reading of Bushnell's Law above.
One is familiarity. Says Barsom, "A certain familiarity -- similarity to music one already knows -- can play a role [in making a song catchy]. Unfamiliar music doesn't connect well."
It makes sense: the effort required to grasp a new musical concept, genre, or approach makes the higher-order work of just feeling the music hard to access.
Familiarity relates to another of Barsom's observations: repetition. Catchy songs often have a "hook," a musical phrase where the majority of the catchy payload resides. Indeed, the itch usually lasts only a few bars, sometimes annoyingly so.
But games rely on small atoms of interaction even more so than do songs. The catchy part of a game repeats more innately than does a song's chorus. In Tetris it's the fitting together of tetrominoes. In Diner Dash it's the gratification of servicing a customer. In Drop7 its the mental calculation of a stone's position. It is also in such tiny refrains where these and other catchy games revisit familiar conventions.
Another property is what Barsom calls a "cultural connection." When a song attaches itself to an external concept, sensation, or idea, it seems to increase its ability to become catchy.
The Beach Boys' catchy songs connected new-found ideas of summer and beach life to more complex themes of longing and desire. When Katy Perry sings about kissing a girl in the same year that witnesses controversial legislation about gay rights, she creates a less charged mental space for mulling over such questions.
Cultural connections help habituate ideas. They give them form, acclimatizing listeners -- or players -- to the social contexts in which ideas might be used. In 1972, Pong introduced the world to the idea that computers were about to become machines for exploring ideas and interacting with people. In 2006, Wii Sports reactivated the den as a social space for families, recuperating the lost digital hearth of the Atari/Intellivision era.
With music, we embody catchiness by running a song over in our heads or tapping a foot. With games, we embody catchiness by playing again, for specific reasons.
Isn't "catchiness" a much better verbal frame than "compulsion" or "addiction" for the kinds of positive feelings of homecoming many games offer? Game designers talk openly about how to make their games "more addicting"; Viacom even operates a game portal called AddictingGames.
Why would anyone choose to call their craft "addicting," a descriptor we normally reserve for unpopular corporeal sins like nicotine? Why would we want game design to sound like drug dealing, the first "easy to use" hit opening a guileful Pandora's box of "hard mastery?"
The rhetorical benefits of "catchiness" alone suggest its adoption. Wouldn't you rather tell your mother that "Drop7 is a really catchy game," instead of comparing it implicitly to a narcotic?
But moreso, I don't think most game designers really want to make games that are "easy to learn and hard to master." A game that's easy to learn probably isn't a bad thing, but it doesn't get at the heart of the sort of appeal that leads to catchiness.
We have plenty of games that are hard to master, and they are not the that ones normally earn the label of "casual." Metal Gear Solid is hard to master. So is Spelunky. Ditto Ninja Gaiden. Striving for a design that demands mastery isn't bad, it's just that it's not the goal served by the designs that adopt Bushnell's Law.
Mastery is a very specialized carrot that works only in extreme circumstances; indeed, the ludic sublime is probably a very rare terrain. Most of the time, creating habituation is enough: making players want to come back to visit your game, whether or not they want to eke out every morsel of performance from the thing.
So, let's end the era of Bushnell's Law, not because it's useless or base, but because it's wrong. It doesn't explain the phenomenon we have assumed it does. Or more precisely, let's excise the first half, and keep the rest: A game should reward the first play and the hundredth.
How? By culturing familiarity and constructing a habitual experience. By finding receptors for familiar mechanics and tuning them slightly differently, so as to make those receptors resonate in a new way, and then coupling those new resonances with meaningful ideas, practices, or experiences.
By becoming catchy, appealing, memorable, a willing, conscious part of the texture of a player's broader life.
 Cf. David J.M. Kramer et al., "Musical imagery: Sound of silence activates auditory cortex," Nature 434, 158 (10 March 2005).