Just to clear some things up....
The idea of managed care was introduced in the 1990's to combat the uncontrollably escalating costs of health care, mainly because people get medical care that they don't need simply because they don't have to pay for it. HMOs and PPOs both fit into that category. There are differences in the two which cater to personal preferences. An HMO means that you are a member of a specific "network" and don't have coverage for services outside the network. A PPO means that you will have to pay a percentage of your visits in exchange for greater provider access (i.e., not limited to the network of an HMO). It's beneficial for someone who travels and still wants to be covered, for example. "Preferred Provider" means that if you use a PCP who has contracted with the PPO, you will receive a discount.
Both systems are used to control costs in different ways. A PPO makes you pay more out-of-pocket expense. Economics tells us that people will opt not to get unnecessary care if they have to pay more of the cost. An HMO controls costs by providing incentives to the doctors to not provide unnecessary services. The idea is efficiency.
Controversy arises in both systems. In a PPO, if a patient has to pay more money to receive care, some patients will opt to not receive necessary medical care because they can't or don't wan't to spend the money. In an HMO, there is question as to whether or not quality is sacrificed for cost.
Also, you cannot sue an insurance company. Insurance companies do not actually prevent you from getting medical care, but they can refuse to pay for it.
For interview purpose, I think that they are looking to see if you know the basics of what HMOs and PPOs are and that, though they help control costs, they aren't the ideal solution to the problems in health care.