I suppose a better way to phrase it is- why is an NPU necessary? What does it enable these machines to do that a Surface sans NPU can’t?

It can basically handle neural network/AI tasks more efficiently than a regular CPU/GPU can.

And yes, these are business-oriented. But my question remains the same - is built-in AI a feature that businesses, as consumers of this product, are asking for?

Yes, deserved or not, AI is currently on everyone's mind in the business world. Working as a software dev, every client these days asks if we "do AI", so we pretty much have to reluctantly learn and use it. And many of those clients are very protective of their data and don't just want to put them on some web service, like OpenAI. So there's certainly demand for locally running AI tasks.