Ting seems like a great deal for certain users - it's not even a certain type of user - but just certain users period.
Basically the tier system makes it so that those who fall on the higher end of the specific tier end up getting a better deal. While those who just barely push past the next tier end up paying for quite a bit of waste (even with the 5% bonus).
It seems logical to use a progressive system much like the federal income tax. The numbers could be tweaked so that the money Ting makes is similar (since after all, it's all about profit), but it would be a much more fair system where no one actually pays for waste, which would actually make the slogan "Pay for what you use. More flexibility. Less waste." accurate.