Why doesn't my Terminal show 'last login' message?
login should display that message unless it is run with a '-q' option or the file '.hushlogin' exists.

It would be good to know the command line for login.

At the command prompt go ps ax | grep login and you should get a line for each open Terminal window that reads something like this :

login -pf &lt;username&gt; 


or 

login -pfl &lt;username&gt; exec -la bash /bin/bash


Check that out and see what it says.

bash and it's profiles have nothing to do with displaying that message. The setting of the "Shell" preference also makes no difference as login is run regardless of how this is set.

If login is  not being run with a -q option then something else is happening. If you try type -a login you should get nothing but login is /usr/bin/login. I'd also triple check that ~/.hushlogin does not exist.