Pretty self-explanatory, except I'm not sure if you are comparing the services themselves or the events, or the consequences of event convocations. "Chirp" was ("is" presuming there will be another in the future) the Twitter developers conference (held just a week or so ago in San Francisco -- I was there and I thought it was great). I am not involved with Facebook development, but I believe F8 is also a developers event.
As far as "Developers" go, I'd say thatTwitter has a powerful and rich API, and Twitter is dedicated to making it "neutral" for both Twitter and outside developers. Also, you could add "User Streams" -- which was a new developer announced at Chirp.
I'd suggest breaking "Monetization" into its own categorical row, distinct from Developers (which might focus on developer features and developer support).