Can a power failure or forceful shutdown damage hardware?

In the case of shutdown using the button, no hardware damage is possible (noting that corrupted storage content is not hardware damage).

In the case of power failure, damage is not caused by the sudden loss of power. But it absolutely can be caused by the fluctuations of voltage and current, both up (at extreme levels these are called spikes) and down (brown-outs) that inevitably occur on the line immediately prior to power loss as the power company's equipment fails. These fluctuations can be observed often in your house lighting as it flickers before losing power.

In addition, since voltage fluctuation can sometimes occur during normal operation, without total power loss, a high quality PSU or some kind of power conditioning UPS will help preserve the longevity of your equipment.

Dirty power, or EMI noise on the power line, is also damaging to sensitive electronic equipment - watch where you plug in that treadmill or other large motor device.

Lastly, power fluctuations are more prevalent on low voltage (110 - 120 V) mains than on high voltage, such as 220 - 240 V systems.

With modern systems, no - as long as you're using the power button, its designed to have a graceful shut down. There's some possibility of data corruption, since your system would not have the time to save everything it was working on.

On the other hand, the very reason you're forcing a shutdown might indicate hardware or software problems already existing.

EDIT: thats practically a seperate question. Thinkpads arn't cheap for a reason - they're tanks, and have great warranty service. Pulling the cable, and closing the computer, is... well stuff they're designed to do. If you switch off the mains, and turn it back on, the Power brick will handle it, gracefully. Unplugging is within design specifications, hell, i suspect lenovo might have a machine to test just that. I'd say none of that sounds dangerous, outside the risk of data loss.

No.

If you're trying to decide between pulling the power cord and holding the power button down for 8 seconds, hold the button down. Pulling the plug could introduce surges or spikes immediately preceding the actual power loss, while holding the button does not do this.

If for any reason your system is not responding and needs to be shut down quickly, hold the button.

The only case where you ought to pull the plug rather than wait the 8 seconds while holding the button down is if you've spilled something liquid on the system where the risk of electrical short causing significant damage is greater than the risk of problems caused by pulling the plug.

UPDATE for question update: Most damage of this sort is cumulative. As in, it builds up over time. Older, weaker, or lower quality components could be actually broken by such actions, but usually not. Usually such spikes and troughs in the power will contribute to wear and tear which decreases the lifespan of the computer, but does not usually kill it right away.

And with a Thinkpad, or any laptop, you need to remove the battery and the power cord in order to hard shut off like this.

It all boils down to risk: If there is risk of liquid getting to sensitive components while they are powered up, pulling the battery and cord is not so bad in comparison. If the only risk is a virus hurting your files, holding the power button down is not so bad in comparison, but pulling the power cord and battery is much worse.

So, depending on what the situation is, take the appropriate action to mitigate damage while minimizing risk.