Why can't I see httpd in activity monitor nor top in Mavericks?
- Activity Monitor default view of the process list is 'My Processes':
Switch to 'All Processes' in the menubar to additionally see other users' - like root or _www - processes:
Check again in 'Activity Monitor'
If it's still not visible it's not running.
httpd not running is default for Mavericks client and server.