I can see very strong use cases for each approach - can it not be an option? I mean, if the advice is "just keep an eye on it and cut the service yourself once you get close to the limit" then surely "how about I throw you a dollar a month to do that for me, since it's far more efficient that way?" seems reasonable. The people who are at most risk here are those with the least means - it just seems quite unnecessarily unfair.