That may be touring-specific? I have tons of components on my regular bikes that last well over 5000 miles, including spokes/rims/wheels and saddles (derailleurs, shifters, pedals, cranks). Many tires even last 5000 miles, although not the lightweight racy ones I use.
Going across the country you're gonna be hitting way more counties and states than you would even as someone who travels for cycling events. More importantly you're also not on a curated ride. Our club was top twenty and people agonized over the relative safety of certain back roads. Pavement quality, debris, traffic, blindspots, pets. Sometimes they got it right, sometimes wrong. It was an iterative process and some segments were only ever tried once (or twice if people forgot why we said no before).
On a cross country trip you don't have locals curating for you, so it's going to be more wear and tear.
Also, with heavy load (bike+luggage for me was usually in the 35-40 kg range) and more riding in rain than I would do when not on tour, leads to increased wear.
My worst failure was a cracked rim on a rear wheel that I should have replaced before the tour. It had started to wear down due to bad breaks. It was still rideable for another 100k to the nearest bikeshop (this was in southern Spain).
That seems... unusual? I'm at 11,000 miles on my current road bike and I've replaced less than that even though I'm using components designed for weight, not durability. I'm on my fourth chain, third cassette, second rear tire (although both tires need replacement soon), and other than those the only things I've replaced are brake pads. Hauling a heavier load obviously increases wear and tear, but I wouldn't expect it to be that much.
Classic choices are the Trek 520, the Surly Long Haul Trucker, and the Kona Sutra. REI has consistently impressed me with their offerings as well.
For the most part, frames get built with a carefully selected set of parts that balances reliability, repairability, and availability. Weight is really only a consideration for the wheels, and it's pretty far down the priority list even there.
Over 5000mi/8000km, everything is consumable, except hopefully the frame and associated components. I didn't blow up a hub over 7000 miles of touring, but I replaced chains, the cassette, the chainring that got the most wear, a couple of spokes, a rim, a saddle, and maybe a few other things. Oh, and several tires.
Mom and pop bike shop availability is clutch when you're miles from even a bigger town. A touring bike is not the bike to have the latest group set on, nonstandard spokes, or anything that you can't fix, replace, or make a workable substitution for in the boonies. AIUI, if you're touring internationally, you really want 559mm rims; 622mm is much less common outside of North America and Europe and finding tires can be a big problem.
You'll often find that frames get built up with an absolute hodgepodge of components that only makes sense if you consider all of the above, plus the fact that gearing runs more on the mountain bike end of the spectrum.
Components tend to run a generation or two behind bleeding edge, and manufacturers mix and match freely between road and mountain stuff as appropriate to get what they're looking for for durability and ergonomics. A good touring bike usually has mid-range components. Good enough to stay adjusted, beefy enough to hold up to a lot of miles with less maintenance than might be ideal.
All that to say, I haven't answered your question per-se, but I hope this helps you understand for yourself whether and answer put forward by a salesperson is a good one.
Most bike shops aren't making most of their money selling touring bikes. You run a very real chance of dealing with salespeople who are totally out of their depth when you shop for a touring bike. The ones that are both good and also honest will admit as much.