It wouldn't suprise me if you saw 15* and 21 or 22* marked at 3, but 18* is strange (15* obviously being a 3 wood.) No, those are pretty common lofts - check the OEM and component sites - all irons have basically the same loft, within a degree or as much as two, but you'd be hard pressed to find a new 18* 3 iron these days.

These days, 18* is standard for 2 iron and 5 wood.