Well it should be noted that when you license an engine you obtain more than simply a binary.

Engines like Unreal 3 and Crysis have well-developed pipelines , quite a bit of well-written documentation , code and artwork samples and other nice things.

Quality, priority support and bug fixes / enhancements. In fact, for certain engine licenses you may be able to make personal phone calls to senior developers , attend or request seminars and meetings with senior engine development staff , discuss and recommend future enhancements ( that are actually listened to, to a certain extent ) etc.

For many studios / publishers paying for such benefits is economical.