Most folk may use a mixer (say) once a week, but if you were to use it 5 times a week then you'd effectively give it 5 times more use than average, which is what it's design life and warranty period take into account.
Then again the average user may use it for 10minutes at a time whilst your use may have been 2mins a day.....
...easy mixing, hard mixing.... all things that impact on its long term reliability
If the device was non mechanical in (user) nature, say a fridge or a television then average use would be more determinable.
Theres lots of factors that can effect reliability and it's hard for manufacturers and warranties to anticipate them all.