It really depends on what the context in the Cease&Desist letter is for.
Are you downloading illegaly, if so, then that is a possible reason you are getting them.
If you are going over your download limit, then they would most likely just fine you. If it happened to be a repeated occurrence (happening 3 times out of the year), you may get a Cease&Desist letter.
They can still limit the download total monthly, you sign up for their terms they have the right to. However, with the FCC placing control on what they can and can't do, that is porlly changing soon.