Most airlines work as follow: Within Economy class there is about 10 different "priceclass" tickets you can buy. It will start from the cheapest ticket that is most restrictive, to a "y-class" ticket that is the most flexible - all economy class. (You can also get V, Q, L, S, T etc tickets all with their own and price and flexibility)
This give the Early buyer and the buyer that is not going to change his ticket the advantage of getting a better price. So, say on KLM you can get a "V-class" ticket which will be very cheap if you book it in advance, but you cannot change or refund it, where somebody else will buy a Y class ticket a day before departure as it will be the only ticket that is not sold out as yet.This ticket will be much more.
THat is also why you might sit next to somebody in economy class that paid 3 times the price that you paid, as you probably booked your ticket long in advance or didnt want the option that the ticket needs to be flexible.
This rule also go for business class, but there is usually only C and J class, where again C class will be a discounted business class with more restrictions than J-class which will be 100% changable and refundable.