Ok, so DASH devs, please explain me how the network knows that masternodes are actually doing their tasks and are not just idling while still receiving their masternode rewards.

This is an important qustion that needs an answer:
If masternodes can idle and are just being paid for a "ping", then masternodes who are doing the mixing and locking are more centralized then in a situation where they can't idle.
Services like masternodecloud.com could just host all masternodes for their customers and not performing the tasks they are supposed to do.

So please, I really want to know an answer to this.