Car power outlets (aka cig outlets) are not regulated -- when on, they are electrically equivalent to your distribution block. The accessories you plug into the outlets usually include a small regulator, as needed. If you want to hook your accesories up to your distribution block, you still need to use the included regulators.
The other key is to note that many 12v power outlets are only on when the key is switched to ACC or ON. Your distribution block is always on. If you hook your radar detector (or other devices) up to the distribution block, you need a way to switch it off when the car is off, so it doesn't drain your battery.