The API sets the rules and regulations of how things interact and who is in control. The success of an API can be viewed as who's rules are the simplest, the most well-understood, and maintains the best control over the entire process. If an API allows a program too much control of system resources and this causes O.S. failures, then that API is not doing its job properly and cannot be viewed as a success. If the API standards are not well understood, programmers will have difficulties writing programs that function properly. There are numerous examples of extremely popular products that are actually inferior to other existing products.
Factors affecting popularity include - cost, style, brand name favoritism, advertising, etc.
The main issues differentiating commercial and home operating systems focus on system security and stability, file accessibility, networking capabilities, and system functionality. System Security - A commercial OS must have the ability to limit, or control, access to the system. Often, login names and passwords are required to go beyond even the basic boot-up screen. The business OS must not crash. This feature is especially important when file-sharing occurs under a networked environment.