Bingo!It depends how you look at it, I think. A lot of luxury services--health clubs, cable TV service (which IS a luxury), etc. are typically paid month by month. Season tickets to sports clubs, big ticket items like computers or TVs--payment plans are common with all of these. So are essentials--you probably pay your rent, cell phone bill, heat, etc. month by month. You could typically save up and pay for any of these but it lightens the load to do it month by month.
In that light, the payment plan is just like what is offered everywhere else. I don't see an issue with it. Maybe some do.
Another perspective is that Disneyland doesn't charge interest, and a credit card does--so by paying Disney instead of paying off a credit card balance, you're saving finance charges.