Connecting to a Raspberry Pi out of the box would be so much easier if it had an UART bridge at the USB power connection. One would simply plug it in the computer and it would show up as a virtual serial port. It would probably also add approximately $1.50 to the price of the RPi.
An alternative solution is to store the wireless network configuration file on the SD card which can then be edited from any computer that can read the SD card. One would simply move the config file from /etc/wpa_supplicant/wpa_supplicant.conf to /boot/wpa_supplicant.conf and soft link or symlink it back to the original location like so:
$ mv /etc/wpa_supplicant/wpa_supplicant.conf /boot/wpa_supplicant.conf $ ln -s /boot/wpa_supplicant.conf /etc/wpa_supplicant/wpa_supplicant.conf
where /boot is the location of the boot partition on the SD card.