That statement in the article is misleading. It's only paywalled while it's in beta. After that he releases to the public for free.
The measly $3/month he asks for pays for him to run a small team of people who analyze boards and schematics, document those findings (also released to the public) and create cores for several different FPGA devices (built upon his own development framework which helps speed up the process). Jotego is probably doing the most to preserve arcade games in FPGA form out of all of the developers who do such work.
I happily pay the $3 every month. Recently Jotego was responsible for producing a finished TMNT core (Furrtek did the board schematics but he dislikes writing cores), The Simpsons, OutRun and more. Moonwalker is just another in a long line of excellent releases.