1) Subsidized office space. You can get an office there for about a grand a month that can house 4 people comfortably. Compare that with the rents in the rest of the building, and you'll find they are much more expensive. What this does is create a density of startups and a critical mass around which an ecosystem has formed.

2) Access to people like Lance Weatherby and other Venture Catalysts. ATDC companies have raised over a billion dollars of VC. The staff helps.

There are fringe benefits, but those are the main ones.