I wondered that myself, especially since it doesn't have to be more expensive to the end user. Instead of selling them 1 month for $6, sell them 12 for $72 or some such, or make them buy a minimum of 10 accounts to get a monthly rate.

Yah, I know the trend is to do a bunch of little micro payments, but its not like you can't do the math for them an say "$6 a month" then when they go to order it, limit the minimum number of months in order to increase the total.