XP is a descendant of Windows 98 (mainstream consumer Windows) which schedules processes from the active window, whereas the NT kernel was originally built from scratch specifically to enable Windows to compete with the multi-user task scheduling environments offered by rivals such as Unix/X-Windows, (i.e. "real" operating systems built up from carefully designed service layers).

Your example compares starting a process directly from a DOS window and from the system command in perl. The latter is an example which is more favoured by the NT scheduling module than the XP model, which presumably had to go into contortions to meet this kind of requirement.

Update: Given that performance anyway varies drastically from one machine environment to another, dependant on many factors, I removed a previous speculation about why it might be 30 seconds.