Some Pricing Confuses Me

I don't know about you, but sometimes the way businesses do things completely baffles me.  Take these pricing games. They probably make sense in some way I don't understand, but I am left confused so excuse me while I rant.

Why is almost every song on iTunes the same price? Also, why is every new CD at a music shop essentially the same price? It doesn't make sense to me. As a comparison, take another product like clothes,  Do we expect every pair of jeans — regardless of who made them or how good they are — to have the same price? Why would we expect the same of music?

Why do book stores put hardcovers on sale the day they are released? After all, they're new. Customers are excited. They want to buy them. They'll buy at full price. Why give them a discount? Isn't this like a movie theater selling a movie's opening weekend tickets at half price? Or a clothes store selling a newly released spring fashion line at a discount while last fall's collection sells for full price?

Why do publishers print the price on a book? Why not let book stores sell it for whatever price they want? After all, if a book store has better service, better trained employees, a nicer shop, shouldn't they be able to charge more? Isn't that how it works with virtually every other product we buy?

Why do airlines charge to check luggage? Isn't it in their interests to have passengers board the plane faster? Carry-ons slow boarding. Now every passenger takes more carry-ons because checking luggage costs dollars. Also, passengers now game the system: they bring a carry-on and when it can't fit it in the overhead bin it's checked anyway — free!