The problem of "change at any time and their discretion" is basicly the legitimate way to abuse.
There should be an extra there specifing that it will not abuse the power of it.
In fact, think about it this way: I work for sony in the contract department. 1 day i change the contracts for 1 month where i will charge 10000% of the regular monthly fee, and send it to my account. Now, since its at the moment "legal" for me to do it, i do this once, and vanish with my new many many millions....
Fine, we know its not that simple, and that ill probably en up in jail, but to give this sort of options is basicly retarded.