That's an assumption that should be the first line of any documentation on importing .CSV text files. I'm unable to find a mention of UTF-8 in the User Guide or anything I've found on importing text files.
Most text editors, including Notepad, recognize several coding schemes and I doubt seriously if I'd have been concerned if I new from the start it was Unicode which is ubiquitous these days. Not saying you need to use one or the other, just advertise prominently what is expected.
Vins