right... with all your experience you're telling everyone that live tiles will bust your cap. don't want to see store traffic? turn off updates. turn off windows updates while you at it. please tell us which apps are still using traffic if you turned off their live tiles. take a screen shot of whatever program you're using to show us the network traffic and what processes.
Well any background traffic runs the risk of busting a data cap. Data caps aren't universal around the world and to assume that they are all huge would be a very big mistake.
Any background traffic can be a problem. It all depends on the user's usage, the cap, and the overage penalties.
You can instruct the user on how to limit the background data use by the OS, but to chastise him as if there is no risk of a live tile, or other background tasks, pushing him over a cap is illogical. Especially since any data use runs the risk of causing a user to exceed a cap and live tiles and background tasks may ever well transmit and/or receive data.
Almost every cap I've seen, and I haven't seen them all, will charge you for an extra GB, at whatever that rate is, even if your overage is only 1KB.