My guess? Data entry. I do a ton of data entry into spreadsheets and almost never need those keys.

Funny enough, as an old school touch typist, I didn't like using those anyways. Having dedicated numbers is nice for data entry, but for formula entry into cells, I'll use the upper line +/- and all that because I'm already using alpha numeric for the cell identifiers. Just a theory, based on use and layout. YMMV.

EDIT: autocorrect needed fixing