I meant, if 5 boxes run cron and one box blows up, only the jobs on that box are affected. If one box is running all jobs and it blows up, all jobs are affected.

That's not really true. With Jenkins, the Jenkins master controls 100% of the execution of jobs on the slaves and Jenkins cannot be multi-master. With cron, each host is responsible for executing its own cron jobs, removing the single point of failure.