I think that the East 737's still have the ovens onboard, but whether or not they are activiated is another question. I know that the ovens in the aft galley of the Airbus fleet (narrow body) are still there but do not work. The forward galley ovens do still work, or at least they were still working the last time I flew them.
When hot entrees are boarded on the narrow body fleet, they are boarded on a ceremic type dish that is foil covered and goes right into the oven. After cooking it is carefully removed with a plate lifter and placed on the serving tray. The only time they board entrees in cooking tins is in Envoy where the meals are cooked and then plated separately.
I know this doesn't answer the original question, but my guess would be that the ovens are present but not activated at this time. Wish Mr. Wench still flew the 737, I could ask him.