Unicode and how it is represented in a file are two different things. Unicode is a good idea, it solves many problems and contains all the (to me) strange characters used by: Greeks, Chinese, etc.
How to represent it in a file is different. UTF-8 is the obvious answer today, but other encodings were tried by different organisations first. The big win of UTF-8 is that you can have characters from very different regions on the same web page (or in the same file) - something that you cannot do you you adopt a purely 8 bit code like iso-8859-1.
We are still in transition: there are files encoded in various ways out there; however I think that UTF-8 will eventually become the encoding mechanism that everyone uses - so files encoded in other ways will become increasingly rare. So: a bit of patience please.