With modern technology, it's completely unacceptable for consumer electronics to catch fire when running it on a bedspread. It should shut itself down when it gets too hot. Worst case, it might break due to being too hot, but it should never catch fire.

I don't think anyone disagrees with you on this.

Apparently the parent comment does as it appears to be blaming the victim

No one knows if this was truly a defective battery before overheating.

The way I read it: CPU gets hot, battery damage from overheating begins, computer shuts off. User turns it on again not knowing the state of the electronics inside. Possibly weakened or damaged electronics cause the battery to blow up.

Bad ventilation weakens electronics and continued use causes catastrophic failure. This is not new.

It is highly unlikely that thermal runaway was caused by the computer overheating.

It's far more likely that a defect in the battery caused this. Perhaps the laptop tried to draw too much power from the battery, and it failed.

The electronics shouldn't allow the computer to be turned back on if it's too hot. If they did, it's the fault of the electronics, not the user.

Well it did shut down according to the article, but it was probably too late.

Because the heat came from the battery, not the CPU. If you just block ventilation, most modern computers/laptops won't break. I had a fan problem with my computer a couple weeks back, it just shut down at some point and didn't switch on again (until it was cool enough). No damage to the CPU or any other component.

But if the battery creates the heat, the sensors for CPU temp will react too late.

There are sensors for battery temperature: my 2011 MacBook Pro appears to have two battery temperature sensors and a battery charger temperature sensor. It's quite possible that in this case the System Management Controller detected the overheating battery and shut down the computer - I'm not an expert on Mac hardware, though.

Routinely blocking the air inlets and outlets on a laptop increases the probability that electronic components will fail over time, though most modern laptops have multiple forms over overheat protection and will throttle CPU speed or even shut down if they get too hot. I should note that all the airflow in a Macbook Pro is through the sides and rear, not the bottom, so setting it on a soft surface would not typically block the vents.

The temperatures that start to increase failure rates for electronic components are far lower than those that trigger thermal runaway in Li-ion batteries. The least thermally stable Li-ion batteries, those with cobalt-based cathodes, are at risk of thermal runaway over 150C. I've never heard of poor cooling being the root cause of a laptop battery fire.

What then is the (likely) root cause of these laptop battery fires?

It's a lithium ion battery. Normal consumer ones have very low but non-zero catastrophic failure rates.