I think the point is that you only really need a wideband to get your tune done. Running it after that is basically just asking the sensor to fry and potentially piss your money away. If you tune the car right on a wideband, when you go back to a narrow-band sensor it will give you the same readings you would be getting from the wideband anyway.
Once your tune is good you shouldn’t be running outside the range that a narrowband can pick up, and if you are it will still tell you that you are way lean or way rich. If you are driving and you get one of those conditions despite your complete tune, why would the more robust information from the wideband make any difference? At that point, something is legitimately fucked up and you don’t need the wideband to tell you what’s wrong.
A narrowband O2 sensor is only good for a very narrow range right around stoich which is not really of any use under any kind of load. Any bossted engine under load better not be seeing an A/F anywhere near stoich or it wil be history. As such, knowing that a boosted motor tuned at say 12.5:1 under load is running at perhaps 13.5:1 could save the motor whereas on a narrowband set-up it would still just be displaying rich while things are on there way to melting. Also, a lot of cars use wideband O2’s as their sensors and as such the sensors are generally pretty cheap and will have similar lifetimes to narrowband o2 sensors, unless of course leaded fuel is being used.