I don't think this is exactly the case. They sell a service. Whether you deem it a service of value or not is irrelevant.
Gambling is heavily regulated for a reason. I would say that games like these should be regulated just as much.
Imagine going to the arcades, playing street fighter II, and it saying "We know you can't get on the score board because you suck, but if you pay $20 we'll put you at the top of the score board anyway". Would that be completely fine and above board?
And yes, it would be totally fine. If you don't like it you don't have to play Street Fighter II. And given that it costs 50 cents a play and has a steep learning curve, that's effectively what they do in a roundabout way.
I don't think it's about being puritan, it's about protecting the most vulnerable members of society from themselves.
For example, say you get 95% of the way through a game, then the game asks for $100 to get past an absolutely impossible stage, they'd probably get a fantastic amount of people spending the $100 reluctantly. Which IMHO isn't a nice way to do things.
But that aside, thankfully capitalism doesn't require you to find a "nice" way of doing things. I'm as addicted to shaving as any player is to a Facebook game. (We could both stop, but don't want to.) I'm even more addicted to food. But that doesn't mean Gilette and Whole Foods are scammers.
Having said all this, it's clearly extremely lucrative to setup games like this.