Because 60-lbs pulling square against the board is very different than weight at a right angle from the mounting.
No it isn't. I won't go thru the whole analysis of forces applied in a cantilever situation as I would when teaching a mechanics of materials or statics and dynamics course, but when a load is cantilevered, the forces on the board are as follows:
-The downward force is thru the center of gravity which would be slightly more than half way up from the socket. The lower screw attachment points are in compression and the upper are in tension. This creates a bending moment on the board of about 4-6 inch-pounds from those forces
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Now we have the CPU hold down forces which also create a bending moment between the mounting screws. Just like you standing on a 2 x 4 between 2 cinder blocks, it is trying to bend the 2 x 4, and it does, that pressure is creating far greater bending moment (> 60 inch pounds than the above
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So warnings about a heavy weight sitting on a desk, a desk being bumped or riding on a car seat are simply FUD. And as I prefaced my statement with:
"As long as you aren't shipping your PC via say FedEx Ground and their gorilla handling techniques, you'll be fine."
So what we are talking about in the context of the statement you object to is a relatively static environment as I clearly stated and shipping a PC with an unsecured cooler is a whole 'nother ballgame. Most PCs rarely take more than one vehicle trip and outside of a car crash, going off-roading or something similar, transportation of a PC is of no concern.
Now if you wanna talk an entirely different scenario outside the context of that statement, FedEx Ground for example ... you can go on youtube and see cell phone videos are just about every carrier mishandling packages. Now if you are going to trust your PC to such potential mishandling, w/o taking necessary precautions that's on you.
This is not a measure of applied forces (baseball sitting on glass coffee table) but of momentum and impact loading (baseball being thrown at 95 mph at a window) ... as I said ... whole 'nother ballgame. In a responsible handling scenario which is the context of my statement, we are talking dropping a baseball on that glass coffee table say up to 12-18inches of drop.... with the delivery gorillas, we are talking dropping it off the Empire State Building.
Outfits like Cyberpower ship 1.5+ pound air cooler all the time ... do you think a majority of these systems being returned for new MoBos ? We started building, fixing PCs almost 25 years ago.... in all that time, I have come into contact with or know someone who had a damaged PC arrive just once. The box "made noises" when picking it up, clearly indicating it had been mishandled. Over that same period, I have had three PCs brought in for MoBo replacements because users installed a CPU cooler and over tightened the mounting screws,
1st - One of the washers had a burr on it and when screws where over tightened, this rotated and cut into the MoBo surface. Required new board and CPU as replacement socket 1156 boards were no longer available and MoBo manufacturer replaced 1156 w/ 1155.
2nd - MoBo was cracked from overtightenting screws
3rd - Overtightening the screws warped the MoBo apparently breaking contact in one of the circuit traces or solder contacts at some point and causing a memory error. Or, the CPU can actually lose contact with socket pins from board warping. Loosening the screws returned board functionality.
Not saying that a heavy cooler is of no concern at all, but yes the concern only exists when the machine is grossly mishandled. It's not going to happen when ya dog bumps ya desk ... it's not going to happen when you move the PC from desk to desk ... it will happen when pushed off the back of a truck.
The "heavy cooler myth" is just that ... an overhyped conclusion based upon supposition rather than fact, much the same as "rad fans should be exhaust as hot air risers" or DDR3 over 1.5 (or DDR4 above 1.2v) is '''ooh ooh scary, scary" and will toast your MoBo, CPU, RAM. If rad fans should be exhaust then manufacturers would not be stating in their installation instructions that "for best performance, install as intakes" .... Intel would not have RAM sets on the certified compatible RAM lists at 1.65 or for DDR3 (1.35 - 1.50 for DDR4)
In conclusion ...
a) a user has nothing to fear from a installing a "heavy" air cooler sitting on their desks, moving from desk to desk or transporting in a responsible manner. The bending / shear forces applied under these conditions come no where close to matching that applied by the mounting mechanism.
b) If you can't be in control of the shipping process yourself, make sure to take proper precautions. Remove or secure the cooler with bailing wire using the clip holes in the heat sink and attaching them to secure them to rigid case points... properly label the package as Fragile, This Side Up and insure it
Can damage occur ? yes certainly ... if the package is mishandled, of course. Does it happen often ? Well I think if it did, you'd be able to find 100s of posts that say "it happened to them" and document the cause. Instead we find threads like this:
https://forums.anandtech.com/threads/who-has-actually-broken-a-motherboard-due-to-a-big-heatsink.13550/
So yes, your chances of a problem increase a bit with a big cooler say of you knock the box of your desk, ship it "Gorilla Express", are in a car accident while transporting it ... but in my experience, I see and hear about more MoBo deaths from overtightening than from mishandling.
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