To correct 8che - it depends on the equipment. I speak only of 737 Classic and NG, and certainly it is not necessarily true in the Classic. The database NEEDS the TA as separate data for an airfield, even if that airfield is 'in the database'.
Anthony - no, the 737's I have flown cannot 'deduce' TL, even with QNH entry. DME arcs cannot be flown on all 737s - it again depends on the equipment, and on the older ones the 'arc' cannot even be put into the route. On the later ones, the arc is often in the database for an arrival and it will be flown fine.