What makes Unity (or at least on of the things that) get a lot of user is the fact that it gives you right to publish game using the free version. While it has some limitation(render 2texture mostly, splash screen on PC build, no big deal or watermark on web build that can be blended into your UI) in the feature, the free version has more than enough feature to arm your games to get released in the market. Plus they don't have to expose their assets even using the freebies.

User can make profit with the free version with the expectation that they will buy the Pro version with the profit(and I'm sure they will). Add that with the fact that Unity offers multiplatform capability. If your game make a hit on PC, why dont you publish it on mobiles with a couple hundred of bucks. And when you want to advert it online, publish a demo on the web or throw some facebook API into it and host it on facebook.