C library system-call wrappers, or the lack thereof

Well, given that Solaris (and I believe the BSDs) only provide *libc* ABI compatibility and not syscall compatibility, this allows them to change the syscall interfaces over time by adding glue code to libc. In theory this is something that cannot reasonably be done on Linux (especially since quite a few people are forced to use syscall() to overcome glibc bugs or missing implementations), but can be done on the BSDs because there is only *one* libc for each project.