Well the issue here is if a ISP's modem(cable or dsl or stupid combo modem/router) decides to not play nice and instead of silently dropping unsolicited traffic(no ones home), it keeps saying 'hello, how may I help you?"
I think it was in the Hughesnet forum where occasionally people see their bandwidth draining and the fix was for hughesnet to change the IP of the users modem or something. But of course by the time the users noticed, half of their tiny cap was gone for the day, too late.
I can look in my router logs/live traffic and see all sorts of occasional random traffic. Filesharing, botnets, port probes. My router ignores it but if the ISP were to log what comes down a users pipe 'before' it hits the actual modem or router that could be expensive if it were a targeted attack.
On cable all your neighbors internet shiate is in the same pipe so the modem has to register it, unless of course in the case of a cloned cable modem running up your bandwidth limits and having to fight with the ISP to check their logs that should show two of the same modem macs are on at the same time(registered to you). »FBI Arrests Another Cable Modem Hacker
Lets say your ISP uses an Ad injector in your Connection. Scumbag injection to white spaces on a page or even replacement of a webpages ads.
Mediacom and injection of ads. »Mediacom Injecting Their Ads Into Other Websites
Ignorant Rogers injecting ads/system notices. »www.michaelgeist.ca/content/view/4083/125/
Cogeco meter doesn't work due to wherever the heck they are using to monitor the bandwidth.