With the addition of interface hardware similar to the target runtime system, a workstation running a POSIX OS can become a functional superset of the embedded system. As a result, the application can be conveniently developed on the self-hosted desktop system.
Even in a cross-hosted development environment, the API remains essentially the same. Regardless of the particular host (QNX Neutrino, Linux, Windows,...) or the target (x86, ARM, MIPS, PowerPC, ...), the programmer doesn't need to worry about platform-specific endian, alignment, or I/O issues.