Yesterday I wrote a piece that compared the APIs of Twitter and Facebook. I said it took 3 months to do with Twitter what took 4 days with Facebook, but I didn't say why it was so much easier with Facebook. Mea culpa!
If I don't have to write server software then it goes much more quickly.
With Twitter, I can't call directly to their API from the browser. I have to write an intermediate server app that calls on my behalf, and call that.
Another advantage of the Facebook approach (which is also used by Dropbox, and recently by Amazon web services) is that because I don't have to run a server, I don't have to buy more server resources if my app becomes popular. They take care of the scaling for me. Which seems fair, they're already going to have to scale their server to accommodate my users. Why do both of us have to do it? Answer: it's duplicate effort. No need.