Yes, certain 19.5 and 22.5 can go for a long time, but not longer than 7 or 8 years before the sidewalls start deteriorating, especially if not covered. I've never replaced a 19.5 tire due to treadwear... only due to age and weatherchecked sidewalls.
Even the "regroovable" or "retreadable" tire casings seem to have a limited life in sunny climates, which in my case renders the recappable tires useless for tread renewal.
The original tread was so good on the tires I replaced, my neighbor offered to buy them. I refused to sell or even give them to him, as the casings were a decade old. I wish I had the discipline to cover the tires all the time, or the permission from the local fifedom to build a big warehouse to cover a 24' long truck.
But in the meantime, I can count on spending 4 figures for tires on 1 truck every 8 years, regardless of how long the tread lasts.