I don't think that companies are able to calculate exactly when a product will break down, and thus, build them that way. I'm sure it is possible from a historical perspective to measure what the average useful life of a product that has not materially changed will last.
There are far too many factors involved in what causes a product to break down. Anything mechanical is going to be prone to break down eventually. Properly maintaining a product will extend its useful life. However, some products may have had problems during the manufacturing process that are not readily identifiable at that time, but do become evident after testing or actual use by the end user. Therefore, many products have some kind of warranty coverage in case the product fails prematurely. If you don't have a good product, eventually you lose sales - not a good business plan. For instance, since your scanner broke down only after two years, does it make you want to go out and buy another Epson scanner? Probably not.