In short, when ya host a website everyone that uses the site technically downloads the pages (thats why new pages take longer the first time, especially wif images) so when you see that the BK home page is approx. 20-40kb (unless changed in the last month or so lol) and has 9,000+ users, that is 9,000 x 20-40kb it all mounts up. So BK would need a considerable band-width.

My site (The Zone!!) only has 3gb bandwidth and i have never came close LOL, although Stevie has the same package as me he has surpased his 3gb already, as he has several videos on his site that users download so they went over the limit pretty damn quick LOL (erm....it was videos of cars before you ask LOL)