There were people who thought it was fun to download one and the same template (the largest they could find) about a hundred times a day. That caused 2.5 GB extra bandwidht every day, or 75 GB a month. With a bandwith price of $1 to $2, you can imagine what such "jokes" would cost each month.
As you probably know, websites do have to pay for the bandwidth they use. So, I had the choice, Eighter pay a lot of money from my own pocket, stop hosting files and images or give everybody a reasonable daily download limit.
I have chosen for the last option. And generally it works like you stated. Users that are not (very) active on this site can download 3 files or some MB limit (which is reached first). People who are registered and active in a positive way and/or share files can download a bit more every day.
I am sure that will be no big issue, since you cannot make more skins for different aircraft in one single day anyway.