i do own both.
first i had the iPT 3G, then i got the iphone 4S and a few months ago i replaced the IPT 3G with the 4G.
i dont think its pointless because i dock the ipod touch on the stereo system which leaves the iphone free to use.
additionally, when im not listening to music i can use battery-hungry apps such as games on the ipod-touch. when my iphone is charging at night i also take the ipod-touch to bed to read up on news or surf the net / facebook.
granted if my stereo system supported bluetooth (which doesn't), the iPad would have been the better option perhaps. still, it does complement my iPhone and i like that i have access to all my apps (not just universal ones) in both devices.