The problem is, it just doesn't matter. Even if 90% of the people making apps came from different industries, if those industries are decreasing, that's hardly Apple's fault. To use the old analogy, the sales of whips and saddles went way down after the invention of the car. What does it matter by how much the sales went down? It doesn't matter.

There's no negative impact. There can't be. If Apple destroyed any industries with their products, that just means those industries aren't things people want anymore. It's not like Apple is giving their products away or forcing people to use them. They're high-end, premium products. If people still wanted a GPS unit, they would buy one. If people still wanted whatever Apple replaced, even if people left their jobs to create apps for Apple, others would fill in the old jobs.

The number isn't counted because it doesn't matter.