You are right - sneakers and running shoes are extremely comfortable. And they last a really long time, which makes them a great investment, especially if you do a lot of walking or are just a "busy body" who is always looking to tackle the next project. Today, most sneakers are made using machines and a factory type process that can crank out hundreds of shoes each day. Specifically, most manufacturers (including all high end running shoe companies like Nike, Brooks, Asics, and Mizuno) use a more modern and updated process called the "cold cement construction process." If you have ever studied the materials used in sneakers and noticed how most look, they all follow a general pattern. Basically, the soles and bottoms of the shoes are made out of a sturdy material, and hold up well to different terrain and can endure a beating for an extended period of time. However, to make the entire shoe out of this same material would not be cost effective, nor would it be very comfortable for the shoe wearer. So manufacturers have created the cold cement construction process as a way to make the two parts of the shoe (the "upper" part and the soles or "bottom" portion) separately, and then bind them together.
Shoe manufacturers and companies can get as creative, dynamic, and ingenious with their designs as they want using this process. This is why running shoes run such a wide range of prices. Some companies choose to get very detailed and put a lot of extra 'bells and whistles' into the bottoms of their shoes, to help them last longer and be more comfortable. For instance, the science used in creating the material for shoes that have thick bottoms that are still lightweight, comfortable, supportive, and flexible gets tricky, and can be very expensive. The upper portion of the shoes, of course, are made out of much softer materials, for comfort and flexibility during the runner's foot strike. Through the cold cement process, the soles are physically wrapped around the bottom edges of the upper portion, and a piece of material is put into the shoe that lines the sole, to help the top portion and bottom portion adhere to one another. The materials are all then pulled tight while the materials are still hot. The cooling process of the materials, as they cool in this new shoe form, help the materials tighten and shrink together permanently.