Read something about cryptography and it'll be clear.
CA stands for certificate authority - it's certificate, used to issue other certificates (either client certificates to replace login/password authentication or application certificates used to encrypt communication with clients).
Using the script from install, you recreated the CA key with different hostname, then you created new snakeoil certificate for apache...
For the dovecot and postfix is valid the same statement as I wrote about the *CA* certificate options in apache / there is no need to set them while you don't use the client authentication with client certificates (not login/password).
Futher reading eg:
http://en.wikipedia.org/wiki/Certificate_authority
http://wiki.dovecot.org/SSL/DovecotConfiguration
