Actually I used COALESCE quite a lot in Firebird 1.5, are you sure that wasn't in IB when they forked the source tree?
Also (not an IB fan, but) the mechanism of returning multiple rows from a stored procedure (usually called currying in functional languages) plus some other SQL "limitations" can help other purposes, like clean, scalable design quite well. I'll never forget some appealing MSSQL features I used years ago that blown right in my face when the system got big.
