Ha! I agree. :-) It was explained in the presentation and in the report from Vision Mobile: http://www.developereconomics.com/reports/developer-economic...

Basically, the definition of tools is third party tools such as: ad networks, cloud computing, cross-platform (e.g. PhoneGap), games (Unity etc) and more.

So, someone who chooses to build independent native apps instead of Xamarin/PhoneGap earns the most?

It would be vice versa: developers who use third party tools (outlined in detail in the linked report) would make more money (according to the survey).

From the original report:

"Only the largest software houses, who can justify the investment required to build their own toolset, can afford to ignore all third party tools. Smaller developers choosing to create their own tools are likely to be left behind with uncompetitive apps or too much time wasted."

I agree as well. This is one of those correlation != causation cases.

The slides don't imply causation though.

The way I understood it, it's an interesting observation that might lead you to wonder what then is the cause: something that causes both profit and tool use.