You're right, in one sense. Part of it is the same effect that results in four gas stations on one intersection, part of it is the presence of resources and connections, and part is that success breeds success.

On the other hand, my attempt at a point was that once you've started your business, you have to focus on it. Suddenly all that other innovation around you stops being opportunities and starts being distractions. If anyone says to you, "What you're doing is stupid, you should be doing what those guys over there are doing," you probably shouldn't listen to them. The last thing you need to be doing is chasing instead of being chased.

"The bubble" is a really good way to describe it.