I don't think you should be fooled as to how many books you sell a day - rather how many books you sell a month. According to the OP he sells dozens of copies per title per day without marketing. I have now published 12 books since in the last 6 weeks and according to my sales I will be fortunate if each book racks up 5 sales a month. So Kindle is not as easy or as simple as the OP makes out - unless you hit the jackpot and write something that goes viral.
One of the guys posted earlier in this thread about publishing lots of books and making small change out of them, and eventually it will build up to some decent income each month. I think he hit the nail on the head. But it's a long and hard road with a mammoth amount of work involved. I am a professional writer - that's how I earn my living, so I write all the books myself in various genres, so dismal sales is not as a result of bad quality.
The OP makes it sound so easy and perhaps he has some secret sauce as far as finding the right niches, using clever keywords, and even more intelligent marketing. But for the ordinary guy or gal starting from scratch be prepared: it's a long and hard and steep road ahead.