That is very much possible. It is also completely impossible when you live in a country where Microsoft decreed that the C in CSV stands for semicolon; as far as Excel is concerned (no, seriously). Welcome in the Netherlands!

Now whether or not Excel can open a CSV file depends on the locale of the user, which will inevitably vary, and of course, whether they are using Excel at all.

So yes, you could offer just CSV, but not if your user is a spreadsheet jockey and you would like to stay on good terms with your support staff.