It's a poor article, significantly lacking in context. BOS, unlike PIT or STL, hasn't seen a big reduction in cities served: other airlines have grown as AA shrank, particularly B6.

http://investor.jetblue.com/phoenix....030&highlight=

From the link, emphasis mine:

JetBlue has added an average of five new destinations per year from its Boston focus city since service first launched in 2004, and now serves more cities than any other airline in Logan's entire history as an airport.