Re: How come...? @Jeffy
"This [metered connection]should have been built into the OS at least five years ago, if not ten."
The metered connection option was introduced 3 years ago in Windows 8, and it is easy to set: right clicking you wireless/3g network connection and just select "set as metered connection".
Windows Update and some other OS features like Onedrive can be instructed to not download/sync when you're using a metered connection. Similarly 3rd party software can use the API and restrict network usage.
I think this option would have been built into the OS 10 years ago if someone had come up with the idea! Where were you 10 years ago? ;-)
That the feature is not (yet?) in any other OS is likely not due to coding challenges.