Maybe they will get money from developers of the APIs opting into their service. As in, give us $X a month, and we will handle all your embedding needs and get your content out there to a ton of different services.
Like, think if Embedly was used for some music recommendation application that pulled together results from Last.fm, Pandora, Grooveshark, and Mog. If I was a developer of an up and coming music playing/recommendation site, I would definitely pay some dough to get included in that group for the web application. It's a win-win, the developer of the mashup gets access to a greater variety of content, I, as the developer of the new music service site, get my website's name out there, and Embedly gets money in the process.
But if I, as a developer of a mashup, wanted to use this new music recommendation site and Embedly didn't offer it because that site didn't want to pay up, I could just circumvent Embedly and go against the site's API directly at little cost.
Like, think if Embedly was used for some music recommendation application that pulled together results from Last.fm, Pandora, Grooveshark, and Mog. If I was a developer of an up and coming music playing/recommendation site, I would definitely pay some dough to get included in that group for the web application. It's a win-win, the developer of the mashup gets access to a greater variety of content, I, as the developer of the new music service site, get my website's name out there, and Embedly gets money in the process.