Is it true that you want a binding that (when you add the low and high / 2) averages to the setting you actually want.
Ie. If you need a DIN of 10, would you want your bindings to range from 4 - 16?
A couple of things:
1. "Is it TRUE", no. There is no real 'need' to have 'extra' DIN above the setting you require. A DIN of 10 binding will work for someone with a 10 DIN.
2. "you WANT a binding that..." personally I want headroom over the setting I ski at, I also want the stronger build and generally better design* that a race binding offers. The difference in design between a binding with a DIN range of 3 to 10 and a 6 to 14 or higher binding is often major, the lower DIN bindings are usually very simple when it comes to the way they release. I really don't think anyone needs to worry about the composites used in regular bindings, however. The talk of metal bindings is way over-blown, but it comes with the high DIN range, so what the heck... if you need it it's there.
3. If you ski a DIN of 10, a binding that goes to 14 or even 12 will work just fine, what 'race bindings' offer is often reduced release modes. The upward release functions are very often blocked or completely missing, good if you are very aggressive and out of balance, bad if you like your ACL ligaments.
*better design = less chance of coming off, this greatly increases the chance of a twisting injury, so better is subjective.
If your DIN number is in the range of the binding, the binding will work for you.
I have found however that bindings that go to 16 or 17 seem to be better built than ones that go to 10, exceptions being all metal bindings (I haven't seen any modern all-metal bindings that only go to 10).
I use a DIN of 8. My bindings range as follows:
Tyrolia 490 with a DIN Scale with tick marks at 4 t0 10.
Fischer FR12 with a DIN scale with tick marks at 3.5 to 12.
Tyrolia FF 17+ with a DIN scale with tick marks at 6 to 17.
Marker Comp 16 with a DIN of 6 to 16.
These bindings do have room beyond the scale, but I've only ever cranked the 490 s past their scale.
This is exactly what I have always aimed at. I'm not sure it's actually needed but it can't hurt to use this approach.