The major difference between stove cooking and oven cooking is that on the stove you will have a hot spot on the bottom and a cooler spot on the top, and with an oven the heat comes from all sides equally.
When making a stew where the meat is in pieces submerged in liquid then you are absolutely right that there's no major difference in the flavor or texture of the end result as the circulation of the liquid due to heat imbalance and movement of the pieces within the liquid will cook things evenly. Where an oven gives a better result is when the ingredients do not have the opportunity to move around, for instance a big chunk of meat, where you will have one side hotter and one cooler for a long period of time as you will end up with one side more cooked than the other. In an oven you would get more even heat and more even cooking of the large piece of meat.
The only exception to the above is when you are going for a long slow cook. I have found that I don't get good heat and ingredient circulation on the stove when the temperature gets too low, I end up with overcooked ingredients on the bottom and undercooked on the top unless I stir often, which is why I will use the oven in these cases.
There are other advantages to oven cooking:
- Better heat control: you can set the oven to a specific temperature and have it be consistent over long periods of time, with a stovetop it's much more guesswork
- Frees your stove for other things: stews tend to be in big pots which take up a lot of space, cooking in your oven means more stovetop space
As for energy efficiency of stove versus oven there are many variables to account for: energy source, pan size and material, ambient temperature, etc. My instinct is that the oven would be more energy efficient as it contains the heat more while with a stove you lose lots of heat to your environment. I have no documentary evidence to support that.
