Those running higher temps may not see problems for a while. Running ICs at higher than optimal temperatures does not kill them immediately, rather it shortens their life. Likewise for hard drives. You can kill them quickly if the temps are way too high, but normally what happens is that the Mean Time Between Failures (MTBF) drops.
So if you have 100 units running within recommended temps, you might have 3-5 failures due to various reasons.
If you have another 100 units running 10-15 degrees above recommended temps, you might have 15-20 failures over the same time period.