Actuallyreal ebony forend tipsand grip cap do serve a function as well as adding some "class" to the rifle.

Ebony is much much more dense and harder than walnut so it resists dings and dents better than walnut would. The place it on the forend tip and grip cap because these are the two places on a stock that seem to get banged into stuff when hunting and shooting.

People also use other types of "hard" woods as well but black ebony is by far the most popular.