That's similar to saying that you never know whether you'll hit the jackpot on a slot machine in Vegas. On one level that's true, but the other plain reality is that the odds are stacked against you coming out ahead. When you buy extended warranties you are betting against the house. The problem is, the house knows the odds, and you don't. Just like in Vegas, they make sure they win. Even so, lots of people play slots -- so what do I know?
But this isn't a casino situation where you're looking to make money. It's about peace of mind. That's the whole point of insurance. Otherwise we all wouldn't carry health insurance (at least in the U.S.). And you have to weigh the cost against value. $65-70 with an additional 2 years for a Mini or iMac is worth that peace of mind in my opinion.
It also may be false that Apple is making so much money on this. They may be providing it as a service for their customers who want this protection at a modest or break-even point for themselves.