Academic operating systems generally follow the Unix system interface, and are developed for RISC machines. Unix has more system development tools than Windows, they are also available with less restriction and have probably already been ported to multiple platforms making the job of the researcher easier. The RISC architecture is chosen for its simplicity, and the x86 is avoided because it is a fucking pig. The overwhelming concern of Operating Systems Research is improved performance. In a multiprogramming environment multiple processes and users share system resources, so there must be a mechanism to protect users from each other.
Research aims to reduce the overhead imposed by the operating system.