I'm beginning to suspect that you're trolling.
Surely you've seen the top right corner of the forums page just above the shoutbox running advertisements that range from Eden Eternal, DK Online, DDtank, Wartune, and others. Throughout the various pages of Aeria alone, there are horizontal strips of advertisements for the games that they host.
Wartune is also at the top of the list on Aeria's splash screen for browser games.
The same principle applies to websites such as Coca-cola and Pepsi that make money just by people visiting them or clicking the respective "like" button. If you'd like to know more about Viral Marketing and the profits made therein, there are plenty of classes available at a local community college.
As for the fixed limit of things that can be done in a day, not entirely. Spenders can buy more raid attempts, refresh their cooldowns on research, crops, and construction.
I am not expert in internet marketing but my understanding is that this is how it works:
Party A has a website,
Party B (a third party) wishes to advertise on Party A's website,
Party B pays Party A for said Advertisement on the amount of clicks made through Party A's website (known as pay per click or ppc ),
As Party A's website gains popularity, it is able to charge more for it's ppc.
The difference between this model and what happens with Aeria is that there is no third party, no Party B. All the game links you see are to games within its own site, they do not link back to developer site. That is not a means of generating income for Aeria.
Aeria pays a licence fee for it's games, it also incurs expense managing the games, testing, managing updates etc. So it is only natural that it selects games that are able to generate income. However, since the games are not developed by Aeria, the in game prices are set by the Developers. Remember the developer generates income through licensing out and through players spending on it's own gaming site, so it sets the prices based on it's own income generation models. The developer's costs include developing the game, maintaining it, managing the licence(s), and promoting the game. It might have alternative means of income but that doesn't help the publishing companies who need the game income too.