Indeed. If ever that they would lessen the 4-second limit, then I think it would bombard the system with reports and would take a long time for moderators to approve and review almost 60 reports for a min (if you wanted to make it a second limit). And 4 second is enough, even the 1 second request per page must also be enough, to somehow prevent crashing the system as well.
Even if you don't even load the post itself, "Report to moderator" and "Submit" means 2 requests to the forum already. So you won't be able to do more than 30 reports per minute anyway.