...but if it costs too much for the carrier to give you the higher speed/volume of data while roaming to not put such limits in place, they don't have to justify it to you. I am sure it is in the fine print of your user agreement. I assure you that nobody tried to pull a fast one on you. It is impossible to predict how much data a user will use month to month. US Cellular is a regional provider and relies on roaming agreements outside their native coverage area and have to pay their roaming partners for you usage.
Im from the midwest and have u.s cellular. I recently went to college in california and have been using my smartphone for many tasks. then, one day the data on my phone was slowed down drastically. I called us cellular and they said i only get 200MB a month of roaming data. That means of the 5gb worth of data i use per month, almost all of that is unusable.
I was not told this when i asked about service in california while signing up with them, and for Us cellular to call themselves a "national carrier" yet limit the west coast's experience with a smartphone seems like a whole bunch of bull.