At this point, the disk surface is going to start wearing out loooong before any of the moving parts wear out. None of the moving parts are going to wear out after 35,000 hours/4 years. The bearings on the spindle are designed to last for decades and the bushings for the head arms will last pretty much just as long.
I've never had a hard drive die from a bad mechanical part, actually. They die from bad sectors or bad circuit boards more often than not.
That has been my experience with all except for one of my drives but that failed after 100 hours of up time. So the only time a mechanical problem has cropped up has been at the very beginning of its life. Also I have drives with 31,000, 35,000, and 38,000 hours respectively in my server and they still work just fine. Not only that but they've been spun up and down on average about 1,300 times in their life.
Drives have a limited number of hours. Its about 35,000 hours or 4 years. That's your evidence. Moving parts wear out
All in all this is a great example about how I don't think you know what you're talking about. You spitting out some random numbers that came out of your rear end is not evidence...
That's like saying that the average human age is 60 years therefore all humans die when they reach 60. You're not making sense, drives fail when they fail. There is no static number on it however there typically is a MTBF number, but keep in mind that is MEAN time before failure, or in other words, the average amount of time that's expected for a drive to survive and for all the drives that WD claims a MTBF for, they are all in excess of 1 million hours.
This is my way of saying, stop spreading false information and do some research.