Maybe it is a testament to the pull of the brand, but like has been stated by another poster, it is about the competition for me. If I sign up for a race with 100 people, its probably unlikely that I will get the chance to "race" against anyone. I'm not fast. However, at an IM branded race with 2000 competitors, I will more than likely end up side-by-side with another competitor, which will give me that slight adrenaline boost and allow me to push my body a bit harder. For me, that is what it is about, not the quality of the roads or nature of the course. All the people competing on that deal are dealing with the same problems. I sign up because I want to compare myself to all of the others on the day, on that course. I'll gladly pay a bit of a premium for that over half the price for a low key, more local grassroots race with 100 competitors.

Or, I could just be a sucker. Who knows.