In order for the good products that actually, work, advertisement is necessary. Very few people purchase a product just because they saw it on the shelf because the majority of people are shopping for specific items while at the store. Even if the manufacturer does minimal advertisement, it should significantly boost sales if it is truly a good product, word of mouth will get them sales in most cases
It is important for companies to get the word out to the public about their products. Even though people may spread the product by word of mouth if it is a good product, it is still important for companies to advertise to inform the public of why they need the product and what it will do for them.
A product can be exceptional, but if no one is aware of it then it might as well not exist. Even the greatest product in its market needs some form of attention drawn to it. How else will people know about it? Many amazing products fail not because of a lack of quality, but because of a lack of advertising.
All products need advertising. Good products are simply easier to market. Good products still need to be addressed by the manufacturer in a way that appeals to early adopters. The early adopters may then go out and tell their friends about the wonders of the good products, but the initial seeding of interest must come from the company itself.