[Soundgod]

Kim, that is right. If you already have a 5 day hopper (which is the way to go) you will only pay another $3 to add the sixth day. In fact, for $6 you can add the seventh day as well (something to consider).
The MYW ticket is front loaded so that you pay full price for the first day or two and then it drops dramatically after that. They really hit day trippers who only want to go for one or two days.
Part of the reason is that you're already staying on property (most people anyway) Disney is going to have the extra revenue from 5 nights in one of their hotels and often times 5 days of dining plan. Also, by the time you get to the maximum 10 day ticket, you're not that far from the cost of a seasonal pass.