That is just how FileVault2 (introduced with 10.7) works.
You have a pre-defined set of "Enabled Users" that are allowed to decrypt the boot drive, and those are the users (just your account in this case) that get listed in the first boot screen. Since you have only one account the system deduced automatically that only your account would be the one to unlock the drive. Since the users are predefined, Apple felt it best to just display the accounts in a clickable list.
The reason for this is if you had multiple accounts on the computer, but only wanted a select few to be able to unlock the drive you could enable those specific users and make it so the others required additional authorization from an enabled user.
OS X also has a handy little helper in that OS X will pass the login info that you gave it during the boot drive unlock into the login window and bypass that screen so you don't have to type in your user/pass twice.