Your premise that the child process doesn't call exit is wrong. Either it exited properly by calling exit with an exit code (setting $?'s high byte) or it was terminated by a signal (setting $?'s low byte). There's no other way for it to exit.

I thought exec executes a system command and never returns..

Same goes for the call to exit it's replacing.

Also, why is 'exec' preferred over 'system + _exit' ?

You're creating a process whose sole purpose is to do nothing but create a process, and you're doing that for as many hosts as you have in your array. It's wasteful! It also requires more code and introduces problems (refer to the bug I mentioned it fixed).