Streaming TV is download. Anything you 'download' from the Internet [and upload for that matter] counts against your data cap. Streaming video sucks it up a lot quicker than just about anything else. Regular web browsing doesn't use up too much whereas video uses up a lot. It is what it is.
Like HfComms said, "cutting the cord" may allow you to not have a cable bill BUT it will take a HUGE bite out of your data. Outside of the Freedom plan (only in very limited areas at the moment) our plans currently are not very tailored to cutting the cord. Early next year with ViaSat 2, we will see plans that are more designed and have the capability to cater to streaming.