Yes, that makes up the majority of my income. The companies pay for the legal rights to use/distribute the games, or to "sponsor" them as it's known. Sometimes they want some branding or an API integrated, too.
I don't see how sitelocking would really work with HTML5 games, so I'd assume the revenue primarily came from sponsorships, i.e. a sponsor pays to place ads and links to their site in your game (usually preloaders, inter-stitials) and 'More Games' links), which are then distributed far and wide.