However, most development tools don't work that way. Most simply give you the full engine, tool, etc., and then it is basically on the honor system if the license is valid and you are following the terms. This is the way ImpactJS works, for example. Obviously, the risks if you ignore the license are very real, and it often times isn't that hard for an engine/tool vendor to tell if you used their product. Most game developers are making a game so they can release it to the general public and have it seen by as many people as possible, after all. Then they simply check if you are a license holder and send you some nasty legal letters if you aren't. Serious damage to the product owner could even result in massive lawsuits.
Is there something specifically you wanted to know more about? All I could really give so far was just generalities.