Quoted from jeffspinballpalace:
TWD could have been named Dead Walkers and sold just as well. Speech and sound did not come from the show and neither did playfield art. Guess there is no way to tell if it would have sold same numbers with alternate title. TWD sales were slow at first and code was a borefest. Some were saying TWD was a throwaway title, like Mustang had been. When Lyman took code in a new direction, interest in the game was rekindled and turned from cold to a warm embrace.
I'm not so sure about this. When TWD dropped, one showed up at a local hipster bar that never had pins before (or since, for that matter), and I'd pretty much guarantee they put it in place b/c of the theme, and weren't sweating the quality of the code. I'd bet that with TWD, as with most pins, theme-based sales more than cover the licensing cost.
I'm all for it if companies choose to make new, unlicensed themes. But I also respect that they are businesses that need to make money to keep the lights on and the investors satisfied. And there's no real financial upside to going with an unlicensed theme. If you do one, you're doing it for the creative freedom (or if the rumors about Steve Richie's next pin are accurate, to keep one of your stars happy), not because it compares favorably vs. licensed themes on a financial basis.