Somewhat. Standardize, yes. One caliber, no way. Fewer than many shoot, yes.
I shoot and load for .45 Colt, so wouldn't buy a .44 Mag. I shoot 30-06, so don't own .308. When my son started hunting I got a used .243 for him, but haven't picked up dies for it yet. He'll be using the 30-06 soon enough (and maybe I'll use the .243, or save it for my daughter).
When 40 S&W came out, I figured I had a nine, and a .45 ACP, and I didn't see much added utility. I might like a small revolver in .327, but, again, don't really see that much added value.
Some of this is for safety, less possibility of confusing and putting the wrong round in the wrong gun. Mostly it's my frugal nature, I don't want to get set up to reload a different caliber, store another flavor of ammo, etc.