What then is the difference b/w WDS and extend existing network?

I've got AE (n) and a TC

Because I want to use ethernet from my macbook pro to the TC I've got the TC in the living room and the AE in the bedroom where internet connectivity is. I'm looking as to why when you have the TC extend the AE and make both available as one network why other computers can no longer see the TC over wireless. Also, in this setup. I shouldn't need wireless on the Macbook Pro should I since it should get out via the TC over ethernet and then wireless to the AE?