using some Nagios script to check if service is down

[empowering]

99.999% of directadmin customers will not have any nagios installed on their box. How is this going to help them if they do not have any nagios check scripts installed?

99.999% of admins don't properly monitor, backup, secure or harden their server. I'm not sure what's your point.

In the end it's up the the admin/hosting provider to perform best practices.

If the person managing the machine doesn't have the skills or time, they should look for a manage service provider to assist.

DirectAdmin IMHO is about making end users life easy first, administration should always be second. In addition, each admin like's their own fav monitoring tool.