Excel enables even less technical people than Wordpress configurers. It provides 99.999999% of the solution, and the rest can be done with macros, pivot tables, etc. That's why it's a good example, I'd say.
Extending Excel is a reason to use VBA, not the C/C++/C# most of Excel itself is written in. Extending Wordpress is a reason to use PHP.
In both cases, the merits of the extension language are almost irrelevant; people use them because they're the extension language for a popular platform.
