Think of it like a car - if you lease a car, you are still responsible for all the maintenance, repairs, insurance, etc. DHPP is kind of like purchasing an extended bumper-to-bumper warranty that will pick up any repair expenses for the leased equipment but not necessarily the towing. It has been my experience though, with Dish's protection plan, the CSR can waive the service call fee under certain circumstances (I just had a conversion a couple weeks ago to 61.5 from 129 due to a botched install 2 years ago and was not charged - I was told it would have been $50+ without DHPP).
Unlike a car lease, though, there is no buyout option at the end of the lease. In fact, the Dish lease is really a perpetual lease that you continue making payments after the contract is up, though they will often swap out equipment for newer models after the contract period is up (and sign you up for another 24 months).