I don't think that's to code. You can put insulation between any width of studs, but you can't hang a set of shelves where there's no stud to screw into...

Hmmmmmm.

We built our home in 1981 with 2x6 studs on 24" centers. This was for more insulation in the exterior wall cavity. We also used 1" foam board on the exterior under the siding.

Yes, its to code. Advanced framing. Combine that external foam sheathing and you have a great high R thermally broken wall.

My 20 year old house has 2X6 walls with 24" spacing. It's structurally to code and allows somewhat better energy savings because there are fewer studs to transmit the heat loss.

Done intentionally 3 years ago in moderate NC. Also with a little external foam.

Also California corners and insulated headers.

Wood has an R value of 1 per inch so your stud has about a 5.5 while your insulation has 21. Big difference.

I will say putting hooks in the garage has been a little annoying but otherwise I haven't noticed any problems. But not sure who is putting shelves in a new house (outside of the garage). TVs are pretty light these days but at the same time, big enough to use a mount for 24 inch spacing.

Wall framing with 2" x 6" studs @ 24" o.c. is perfectly fine and allows for more insulation in the walls as others have noted. In our climate zone (zone 4) we need to construct 2" x 6" walls if we're using cellulose insulation in order to get the required R-value.

You'll need extended jambs for windows and exterior doors. I recommend using 5/8" drywall for the walls if you go 24" o.c. to minimize flexing.

We also used 5/8" drywall screwed and with glue and edge bridging pieces for the ceilings. There are many anchor options where a stud isn't available.

Strange reasoning, IMO.

What is strange reasoning? More insulation? Why would making a house more comfortable and easier to keep that way be a bad thing?