You can now login with any key. One of the most common actions that will be performed in the wallet (claim rewards) only requires a posting key.
While it is true that the wallet could exist without any 'login' feature at all and simply prompt for the required key for an action, we believe that something like this would be more confusing to average users.
Keep in mind this is designed to be a replacement for the existing wallet in condenser, and the two separate apps should feel seamless when used together.
Thanks for the feedback @sneak