It may be because, outside of a few domains, we just accept software failing all the time, and hence do little testing of it.

Testing every possible failure mode of a simple full byte wide adder is in fact pretty non-trivial and hard work.

Troubleshooting everything that could theoretically go wrong when asking Alexa to add two numbers is simply impossible or incredibly expensive.

Space shuttle computers for autolanding are possible although testing suites are expensive, as you state. Implementing that process to the same level of reliability using a vast distributed software technology like Alexa would be essentially an infinite cost.

Its a given level of reliability problem; can't compare the apples to oranges of extremely unreliable software or even worse, networked, solutions to something as relatively cheaply reliable as hardware.

I think the implication was that there is less testing needed from the software side.

That said, I suspect it is also a bit misleading. If you are relying on functionality of the hardware for esoteric things, you test them heavily.

It moves the testing around: you don't have to test it yourself, because a huge amount of effort went into that before starting to cut IC masks and each unit is individually tested off the production line.

Gotta test the shit out of hardware features. True.

At the application level, less is needed. Spec will be met.