No, XSite Pro didn't miss the boat. Having a login with saved user name and passwords, etc. requires a backend database. XSite Pro is for creating static web pages and websites. XSite Pro is flexible enough to be extended via addon scripts to accomplish this. You will still need to setup the MySQL database on the server and install the script.
Here's a free script to try: http://php-login-script.com/
There are numerous scripts out there, some free and some for pay. It really depends on how secure you want to be, whether you are collecting payments, etc.