Using the proper settings for encryption also prevents access to the WAP. Using WPA-PSK/AES with MAC filtering is a "belt and suspenders" way of securing your network.
Of course, the best way would be to use RADIUS and a password token (i.e SecureID). But that's way beyond what's needed for the average Joe's home WLAN.
There is more than one way to obtain unauthorized access. For most home networks, it is sufficient to limit the machines that are authorized (e.g., via MAC limiting), without getting to the "user" level.
Encryption is necessary to make it more difficult for strangers to snoop on your broadcast keystrokes.
The problem with this article is that it plants the idea that data encryption instigated/required by the WAP will prevent unauthorized access.