I think the proper way to "rollback" a backup is to do a restore. 😉
No, because that will bring the database back to a previous state. The way to rollback the backup would be to delete the file that was created.
This may be one of those "it depends" things. In my way of thinking, when you rollback a transaction, returning it to the previous state (before the transaction began) is the desired outcome. So restoring the database after a backup is like rolling back a transaction. They both return the database to the state prior to the respective action.
I see what you are saying though because if the database is live a restore would lose all transactions from all users that occurred after the backup.
But if the database was in single-user mode during a maintenance window or something than the effect of a restore is the same as rolling back a transaction. And this is one situation I can think of where a DBA may want to "rollback" a backup. Something went wrong during maintenance and he or she wants to start over. But since you can't rollback a backup the next best option is to restore. In this case, trying to rollback by deleting the backup file would be disastrous for the DBA.