Is a calorie burned the same no matter how you do it? Sleeping, running, walking, swimming?
Absolutely NOT! I can tell you from personal experience that HIIT/ crossfit/tabata style cardio will burn WAY more fat than standard slow cardio.
If your doing the old school slow cardio, fasted empty stomach is best. The energy demands are low and you body can pull stores from fat etc.
For HIIT/crossfit/tabata you generally have to do it at least a couple hours after eating, you will likely puke if you do it on a full stomach.
The key to HIIT/crossfit/tabata style cardio is called EPOC (Excess post-exercise oxygen consumption) and its the phenominon that after extremly hard cardio activity you body will continue to burn calories for a good 12-24 hours AFTER your workout.
On a pur calories burned during a workout comparison slow cardio appears to burn just a tad more, but in practice it doesnt hold a candle to Epoc inducing cardio.
So, why dont more people do it? ITS HARD! You will not get the benefits if you dont drive hard. Also because your driving yourself so hard it can be detrimental to other goals and it does put a systemic demand on your system that will invariably require more calories be consumed.
Personally when I started doing cf style cardio I quickly overtrained (took about 6 weeks) at which point I had to step back and monitor my food intake. After adding in approx 1000 cals a day to my diet things everything was fine and the fat started to melt off.