If you can't kill it with a .22LR or a .30-06, you ain't in North America. Nice to have more options - makes it fun, sells lots of guns and ammo for the manufacturers, keeps all the little cubbyholes on your reloading bench full of things you can never find when you need them - but when you get right down to it, those two are all you need. I own plenty more than that myself, but that's a want, not a need
While I agree that those two will do all your killin' needs (and really, we could drop the .22 LR if simply killing critters is everything), that doesn't mean other cartridges don't have useful purposes.
I think someone already drew the parallel that trying to fill every firearm need with one cartridge is akin to playing golf with only one iron. I submit that golfing with one iron would be easier. Trying to fill every firearm need with an '06 and a .22 LR would be like trying to build houses with a hatchet and a tape measure. It can be done, but not easily or efficiently.
Take those of us who hunt predators; Yeah, the '06 will kill a coyote or bobcat just fine, but then you've got a couple of nasty holes in your pelt. With my .17 Rem., a pinprick entrance and no exit, and they are DRT.
Varminting; Again, the '06 will certainly kill a praire rat or rockcuck, but that's a lot of recoil to tolerate, even with accelerators.
At the other end of the spectrum, we have big things with sharp teeth and bad attitudes. Yeah, a '30-06 will probably get the job done with proper bullet placement, but I personally would have a lot more confidence in my .375 Ultra with 3 tons of energy riding on a heavily constructed 300 gr. bullet to save my skin in the face of a pissed off Brown bear.
So again, while I agree with you to a point, I wouldn't go as far as to say that anything other than '06 is just a want, not a need.