This also came up on the Mahara Barcamp 2014: Microsoft Excel has the strange behavior to determine the separation character based on the system language setting, which for German users turns out to be a semicolon instead of a comma. Therefore, CSV-files generated on a German-set windows usually cannot be imported directly but have to be opened in a plaintext editor and the semicolons replaced by commas. Alternatively, the language setting in Windows(!) has to be changed before saving the document as CSV to export the file correctly.
Apparently, Moodle lets you specify if your file is semicolon-separated but I think it should be easy to check automatically, if the first line is separated by commas or by semicolons.
Any system for auto-detecting the delimiter would need to have a confirmation screen to make sure it has detected the delimiter correctly. Since that would require an extra page-load and extra click anyway, I think it would be better to simply copy Moodle and have an option for the user to say "semicolon" or "comma".
Or if we wanted to get fancy, have some Javascript attached to the file upload form, which examines the file, guesses the delimiter, and ticks the appropriate box on the form.