The business model for Epic Games certainly has changed. There was a time when license for the Unreal Engine was over $1 Million and now the latest version is absolutely free. This is great new for casual game developers - as well as mainstream publishers as it will allow them to make games cheaper. Ok, while games won't be cheap, it will at least ensure that a lot of people use the same platform and that modifications should be pretty easy to do.
Sweeney also states that everyone who paid for an Unreal Engine 4 yearly subscription will get $30 worth of credit free to spend in the Unreal market place, which is one heck of a deal. All in all, its an epic (pun intended) win for the company considering that the deal is bound to attract new Unity developers and since the tool is incredibly flexible to use, we're likely to see some interesting games in the future as well.