I understand the logic - and I think you will see that there is no one "right" answer. If I had known when I bought my console what all the arguments were - I probably wouldn't have bought it - the arguments for a wrist mounted system seem pretty compelling. But it has worked flawlessly for me and I'm now pretty partial to it.
I'm in my late 40's and I have a UWATECH SmartCom air-integrated console with an analog magnetic compass. I wear it like others here have explained: under my left arm and clipped using a retractor to a D-ring on my right chest. It stays right where it is easy to see at all times with either hand.
Here's what I like most about it: large, easy-to-read display. My old eyes have a hard time reading tiny text and details on a watch-sized computer without reading glasses. The SmartCOM is now 3 years old and has been on about 60 dives, and I still have have 87% battery left on the original battery.
The bad news: I will have to send it back to the factory when the battery eventually needs replacement.
Some folks have reported problems with quick-disconnects. So far (knock on wood) no problems at all with mine and easily disconnecting it from the reg for storage makes it a snap to download data via IR to my computer. The software is awesome - it snaps a picture of all my gauges every couple of seconds during my dive and graphs it for me showing depth (x) and time (y). Placing my cursor at any point on the time/depth chart shows me the exact readings on my console.
My dive buddy has a wrist mounted air-integrated system, and has had several instances where the transmitter and receiver stopped talking to each other during a dive. Sometimes it spontaneously is restored, sometimes not. He inists on having an SPG on a high pressure hose as a back-up for this reason. I'd be far more excited about air-integrated wrist computer if I could eliminate a hose, but apparently its not really a good idea, so where's the advantage? I have ANOTHER piece of gear to worry about and just as many hoses and gauges as before.
To me, my rig seems to make good practical sense - and it works for me.
I couldn't be happier with it and have no desire to change.