It would be likely that someone would burn fewer Calories if they continue to do the same exercise duration and intensity for prolonged periods of time, particularly if they are simultaneously losing weight. The oxygen demands of the muscle not likely increase, but would probably decrease due to improvements in efficiency of the movement. This improvement in efficiency may or may not be substantial.
This is definitely part of the problem with people who plateau during weight loss, or even regress and gain weight back. As they lose weight, their metabolism will decrease. This is rarely accounted for in their diet. On top of this, some trainees will fail to increase the intensity of their cardiovascular exercise over time.
This is one reason why I like interval training. While it does not need to be performed every session, I believe that it allows people to practice training at a higher intensity. I have found that many people enjoy interval training and it will carry over to when they perform lower intensity cardiovascular training.
Steve Teahan, BS, CSCS