This is a frustrating problem, especially since MacBooks have such a high price tag. However:
"The stains start to appear after 12 to 18 months."
That's beyond the warranty period of the MacBook. When you purchase a MacBook, Apple makes it very clear that the warranty will expire after a year. I don't think it's reasonable to hold a company accountable beyond their warranty period if the price and warranty are clearly defined at time of purchase. If Apple products continually fail just outside of their warranty, the market will adapt to reduce the amount people are willing to pay for Apple hardware.
One thing though: Apple always states their one year warranty (and tries to push Apple Care). Legislation in your country might disagree and Apple has to adhere to it. In Europe there are vast differences, ranging from 2 to 6 (!) years.
I'm a Macbook Retina owner myself and I'm not happy. Having a 2500 Euro machine that lasts as long as a 400 Euro crapbook?
Australia has a 'common sense' approach to it. Basically legislation says means Apple has to make sure that their machines must last for a reasonable period of time, considering their price, market power etc. They explicitly mention that would you expect a $400 watch to last longer than a $40 watch.
Apple devices are more expensive than their counterparts, and you would expect them to be made of a high quality and last longer. That's why in Australia Apple provides minimum of two years warranty on all their devices.
EDIT: To expand- you are complaining about people complaining about a manufacturer's product. The natural process of market adaptation that you expect might very well involve customers complaining.
"The stains start to appear after 12 to 18 months."
That's beyond the warranty period of the MacBook. When you purchase a MacBook, Apple makes it very clear that the warranty will expire after a year. I don't think it's reasonable to hold a company accountable beyond their warranty period if the price and warranty are clearly defined at time of purchase. If Apple products continually fail just outside of their warranty, the market will adapt to reduce the amount people are willing to pay for Apple hardware.