I know not to underestimate Mary and crew at the RoadRunners because they do an excellent job.
But I think a lot of this is just numbers for marketing reasons. Crowd estimates are notoriously off.
No way 2 million people watch the NYC marathon live.
The Marathon website says the marathon had a worldwide tv audience of 265 million
http://www.nycmarathon.org/about/partners.php
Total bs.
The SuperBowl gets under 100 million:
http://sportsillustrated.cnn.com/2006/writers/steve_rushin/02/03/rushin0206/index.html
If there are 20,000 in the park for that other race that might help some. If there are 20,000 spectators that will be enough for the runners to think there are a ton of people.
I don't think they could get 200,000 in the park no matter what (unless perhaps it was the day of the marathon, but that is basically Giants stadium *3). But I think with Mary throwing out the 200,000 number some people in the media will think "Oh this is a big event" (which it is)