I would treat modern detectors just the same as any modern electronics.
Most everything (and I mean EVERYTHING) is reflow soldered, surface mount, solid state electronics. This stuff is quite tough. Tough enough that all modern military and "mission critical" grade equipment is made with the same technology.
Now, that said, there are differences. Tolerances of components, quality of components, etc. For example, when resistors are rated, they are marked with a final color coding band indicating how tight of tolerance the resistor exhibits. Obviously, the tighter the tolerance, the more expensive.
There are also environmental factors to keep in mind. Heat is by far and away the absolute killer of electronics. As was mentioned, leaving a device in a hot car can be very damaging to the components. Particularly the display. Heat causes expansion, cooling causes contraction. This rule is exhibited (if even on a microscopic level) in electronics components. With repeated heating and cooling cycles, you can significantly shorted the life of a device.
The other factor is just plain luck. You absolutely never know when a device may fail. Despite a service life rating, it is still completely up in the air. There is also a little trickery in the rating systems. For example, a company may manufacture bearings for large air moving fans. They may rate the bearings at 10K hours under full load. You would think this means they ran a series of bearings for 10K hours without failure. Well, some companies may run 1000 sets of bearings for 10 hours. Or 100 sets of bearings for 100 hours. While this may not make sense, it is a common technique in cheaper product design.
With my new detector, if I take care of it and avoid physical trauma (dropping or beating it up), keep it dry and keep the temperature kinda stable by storing it inside the house, I would expect that detector to work for 20 years. The performance may degrade ever so slightly, but nothing noticeable.
WM