Are you using the standard db API or the (deprecated and before long ripped out, I hope) templating system db API?
Regarding the standard db API, db_multirow puts the value at the template level while all the others put the value at the caller's level. This is an artifact of template integration, I guess (db_multirow is only useful when you're passing a rowset to a template, while the other db_* procs are also used to return values used directly in the calling script).
