If everything is configurable then it will be difficult to support.

Q: Wonder about how the WPS got so configurable?

A: WPS is passive. Either you find the info or you dont - depends on you. Key assignment and usage is a pretty active task that could lead to a lot of confusion if done wrong (delete recursively e.g.)

Q: How about it is only configurable through text files. Then only "hackers" will start to mess with it?

A: It is now, in a way. If you really want to make the buttons do different things, you can edit the rockbox source and compile it yourself. In a way, it is configurable by text files right now. And, only "hackers" can mess with it. I wonder why one wants configurable keys anyway, other than the menus. But that's just my opinion...