Gods and Goddess's in Japanese Religions Options

http://www.scns.com/earthen/other/seanachaidh/godjapan.html

This is kind of a cool page listing a lot of the Various Gods and Goddess's in Japanese Religions.

Shinto (the Way of the Gods) was the original religion in Japan and had no written literature before the arrival of the Buddhists. All true Japanese mythology comes from this religion. Shinto teaches that every natural thing, human, animate or inanimate, has a spirit in various degrees of vitality and strength.

Shinto is also called the way of the Kami which means "Gods" in Japanese. I find this religion interesting because they had no writings so it makes you wonder Exactly where and from who it originated and how it was passed along through all the ancient villages. Sadly with out keeping literature and a time line I know I will never know the Answer.

Another question I have I know this might not be the correct place for it but none the less it does tie in a little I promise.
It seems the most accient religions in all regions began with more then one "god" or "Goddess" and they where all in some form of ranks depending on what they where the god/goddess of and who the originated from. It makes me wonder how a lot of people just decided one day that the accient Religions where not correct and that there was only one "god". This confuses me because surely the older the religion the closer to truth it must be. I suppose its a question no one really knows the answer to... But its still something to think about.

This confuses me because surely the older the religion the closer to truth it must be.

I don't understand this part why does being older somehow mean it is closer to the truth?
I'm not saying that it makes it farther from the truth or closer but how does age have anything to do with it's relation to truth? It appears the opposite for other areas of thought as far as astronomy, medicine, etc..
Just wondering because I always see the claim that earlier or "ancient" practices are somehow more "truthful" but this always seems to be opinion rather than anything tangible. It appears one could just as easily say they are farther from validity due to their age.

Why are multiple gods and ancient beliefs any less "wrong" than current ideas?