It is a case where some small amount-$2-$5 which I will never miss and means nothing to me will make a big difference in someone who is less fortunate(finacially)than I.
I also get a few goodies and perhaps a little more time is spent on my room.
Now at hotels with turndown it does start to add up-but it is still less then the price of a good drink or movie.
So yes-I tip,but if the room is not cleaned well,or supplies not restocked then the tips tend to decrease-til the level is raised again.