on Pencil case and washing the dishes

I always wonder why is "pencil case" called a "pencil case". I mean, that rectangular container does not necessarily keep only pencils, right?

The same thing goes for the phrase "washing the dishes". When one is asked to "wash the dishes", does it mean that you only clean up the plate and ignore the cups, glasses, or other cutlery?

If you think that this is merely a buffoonery in English language, then think again. When translated to Indonesian language, "pencil case" becomes "kotak pensil" and "washing the dishes" becomes "cuci piring" which remains faithful to its original English rendering.