The people who partake in an polytheism belief system often do not claim one god is "the one true god". Normally, these people align themselves or ask for help with the god they think will help them the most. This alignment can change depending on the situation like a mother praying to the god of childbirth or a farmer praying to a god that is suppose to make the ground fertile. This might sound silly but it was a very popular belief in ancient times. The Greek culture, which most of this is based on, had a pantheon of 12 main gods and an uncountable number of lesser gods. Most of the people worshiped many gods while priests limited it to one.
Also the D&D gods do have a great deal of power. They are able to give their most devout followers, templars and priests, special powers that aid them in dire situations.
Personally, I like the pantheon system. It often creates a rich world that is fun to play in.