SVR4 (hence SunOS 5.x) tries to make everybody happy. The traditional (slow) System V "shutdown" runs all the rc0.d/* shell scripts with "stop" as the argument; many of them run ps(!) to look for processes to kill. The UCB "shutdown" tells init to kill all non-single-user processes, which is about two orders of magnitude faster. In old versions of Solaris (2.2 and before) the UCB version did everything it should except actually halt or reboot.
If you run a database (like Oracle) or INN, you should install a special /etc/rc0.d/K* script and make sure you always shutdown the long way.