> Anybody who knows a bit of Excel can pull that data themselves by following a set of simple instructions.

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.

I don't use MS Office, but does Excel seriously not simply show a dialog, where the user can select this and maybe even auto-detects it? That's what I'm used to from the "subpar clone" (/s) from the Document Foundation.