Tic Tac Toe AppEngine channel sample mechanics

Greetings

EDIT: forgot the link to the sample, here it is: http://code.google.com/p/java-channel-tic-tac-toe/source/browse/trunk/src/com/google/appengine/demos/channeltactoe/

So, I am learning the AppEngine channel API, and I came across a question about how it is encoded in the architecture. They, as I understand it, work, the client sends standard POST requests, the game is updated, and both players receive an update through the ChannelService JSON message.

Now I read on javadoc that Channel is a two-way communication channel, so why did this developer go to the POST servlets (for game updates) and Channel for distribution instead of using a single servlet to create the Channel, and then use this channel for front and reverse play updates communication between client and server?

To make the summer what this architecture has done using a real two-way channel, or it is even possible to use a two-way (server back channel) in this way.

Thank you for reading, I hope my question is really / understandable. -Rohan