I think you'll find that these characters (and others) are reserved. For example, used as separators / special operators in URLs (i.e. what you see in the address bar of your browser).
So when ' or = are used in a file name and then submitted over the Internet, the filename is read only up to the first instance of ' or = and so then cannot be found (e.g. freddy's.jpeg is just read as freddy).