It's a lot of local councils making judgements individually on an case by case basis. The rules can vary quite a lot depending on the individuals involved.
It's also important to remember that most Amish didn't choose that lifestyle, they were born into it. And while it is possible to leave at any time, it is pretty difficult to adjust to a radically different lifestyle with little support on the outside. So instead you see stuff like air powered blenders where people work loopholes so they can lead a more comfortable life while not having to go to extremes.
This is the major difference between the Amish and for example Monks. In the latter case they chose that lifestyle and find it fulfilling in itself. They weren't forced into it.