On http://drupal.org/about/new-in-drupal-7, one of the main differences between Drupal 6 and 7 is said to be cron ("More secure implementation for scheduled tasks (cron.php)")
The main difference I can find so far, is that you actually got an interface in Drupal 7 to say how often cron should run. I assume that means you don't actually need to set a crontab anymore.
I'm guessing the settings in the interface're a core implementation of Poormanscron, in case a regular crontab doesn't work. Is this right, or am I getting too confused here?