Your analogy is too far off in scale to work. Constant coffee refills would take days to fill up a tanker truck. If a tanker truck is 1.2TB, then getting a coffee refill every few seconds isn't the equivalent of full speed downloading, it's the equivalent of streaming high quality video.

So the analogy you proposed would say that streaming video is abuse. The analogy is wrong.

Also, when talking about how "most downloads take seconds", video game (re)installs can be over 100GB. You could have two people each install two games and blow out half your data cap in an hour without doing anything remotely unreasonable.