Since the only way to put members into the banned group is in the ACP and not on the warning page (the actual group changing) or the edit member page, it makes it where it's much more annoying to be able to move someone to the banned group. You have to go into the ACP and search for the member rather than simply doing a couple clicks if it were on the edit member page.

You might find this interesting:

http://forums.invisionpower.com/index.php?showtopic=273885

Another reason why IPB3 will be so exciting