I think the big difference can be seen across two types of hackathons: ones that are corporate-sponsered, with corporations offering massive prizes and startup funding for people with "fresh, hip disruptive ideas leveraging their cool web tech", versus small ones that are about creating something neat and showing it to others. Of course, this is a gradient, and things are not black-and-white here.

A lot of small local game jams fall closer to the second category there. I think you are right that financial stakes affects the attitude of the hackathon.