Is Flaps25 an option for take off on the 73? Would you not get the gear horn once you selected gear up?
You are thinking of 747/57/67/77/87
These aircraft have Flaps 25/30 as approved normal landing configurations. So if for whatever reason you were to do a Flaps 25 takeoff, while ignoring the takeoff configuration warning, you would of course get a gear config warning once selecting it up after takeoff.
However, the 737 also has a Flaps 40 setting (just like the 727 did), and thus Flaps 25 is a approved takeoff configuration. Hence no reason for a config warning on gear up selection.