Correct, the jack in the back is input only, just like any BT speaker. So, if you have a device that is not BT capable, but has headphone output, (e.g. an iPod, a portable CD player, even an iPhone, etc.) you can plug it into the Tap to play your music.
On the other hand, a Dot's audio out is for connecting to any sort of audio-in, e.g. to stereo, or to a non-BT headphone.
Basically, the Tap in an input device and the Dot is an output device.