Problem is that smartphones don't really have a unified architecture, and hardware can vary widely. Also, space is limited, so you can't just have a large selection of drivers available with the OS, you need it specialized and streamlined for the application. Windows mobile is an attractive base because its one OS and is easy for hardware and software developers to develop for because they already have experience with it, so they aren't starting from scratch each time they make a phone and they don't have to deal with the added complexity of supporting every (or even several) OS's that all behave differently. Palm has been having this problem trying to support both Windows Mobile and Palm OS based smartphones, and from my experience at least, the Palm OS phones are prone to malfunction as they age. But who really wants to use Windows Mobile?