Supposedly, that statement is correct.
However, I think you would start to get CPU throttling well before that happens. So even if that temp doesn’t fry your SOC it could result in decreased performance and possibly shorten the CPU life span. This is pretty much a true statement for all electronics, the cooler it runs, the longer it lasts.
IMHO if a $14 USD fan can get my general usage temperature under 30 degrees C, which is half of temp_limit=70 or 75, I would consider it a worthwhile expense just to try and get the most life span out of it as possible.
In my experience, there are two things that have a large influence on the life span of an electronic device.
Dirty power or smaller power supplies that are marginal for the device, and high operating temperatures.
Remember, a USB SSD will most likely be an additional load on the power supply. Also, a keyboard, mouse, and maybe a thumb drive on a NON-powered USB HUB would also be additional load.
Take a well designed electronic device, give it clean power and keep it cool and it will probably last a long time.
Pudge