There is a little bit of an apples and oranges effect here, so to speak. High Intensity Interval Training, and High Intensity Continuous Training are not directly comparable by the term "high intensity". If you take the same person applied to both workouts, basically you would find that their HIIT sessions were still of considerably higher intensity than their HICT sessions. Both are called high intensity, but it is a relative term. HIIT should still always be far more intense than any continuous training workout. There is some leeway in this rule in only the most elite of athletes, for example, sub 4 minute 1600m (1 mile) runners. They have trained to a point where they are running an extended time period pretty close to their maximum effort. However, this extended time period is still only 4 minutes, not 20 or 30. Basically, it is impossible for a person to run at the same intensity continuously as they should be running for HIIT. This inherent difference is what makes HIIT beneficial in different ways. Some research has shown that HIIT is the most effective (perhaps only?) way to increase VO2max (or however you type that out) substantially. This supposedly being a significant measure of fitness levels. also, part of the reason for doing HIIT instead of longer continuous training is that there is a time frame for completion of a workout, so to speak. most people tend to do weights and cardio in the same session, but trying to do an extended session of cardio after 45-60 mins of weight lifting means you are putting your body at risk of being overstressed and producing counter-productive hormones. most suggestions call for workouts to be completed in under 75 mins partially for this reason. of course, you cant do HIIT for every cardio session for reasons quite similar.
also, total calories burned from exercising shouldnt be such a stressed factor. long term continuous training may burn more in one workout than HIIT, but you can only safely maintain just so much of a caloric deficit, and the majority of that deficit should come from a healthy diet. exercising extra to make up for poor diet is most likely not going to lead to long term results and overall fitness.
all-in-all, each type of cardio has its place, and picking one over the others will most likely lead to either detrimental (too much HIIT for instance) or sub-optimal (nothing but slow and steady) results. A person must take care not to over-stress the body, while still working it well enough to make improvements. though over stressing may yeild results initially, if kept up things will reverse and get negative fairly quickly. If under-working, stalls in performance are more likely.
I would really suggest taking a look at what Steve has set up cardio wise for TomO. It is a very good example of balancing things out, and I believe Tom has made some amazing improvements in a relatively short amount of time.
Hopefully this helps to answer the original question