Neither the plastic nor the metal likes to be under stress. Some places, especially those prone to earthquakes, tend to move around and can generate stresses. Even on new construction, there may be a little settling over the first year or two, and maybe more often during/after a good shake. The plastic gets a little brittle as it gets older. The metal gets corroded and can crack easier. Nothing is permanent, it's just how often you may get before it does die that differs. Regardless, an access panel makes life easier down the road, but if the walls are not tiled or plaster, cutting a hole when needed in drywall, is pretty quick and easy. Now, it gets messier if it is say paneled, faux finished, or wallpapered, but hey, making the hole is easy!
If you look at the earthquake maps, most places get them, the differences are frequency and magnitude.
