You're placing too much emphasis on excess post exercise oxygen consumption (EPOC).
It is simply a matter of caloric expenditure being greater during steady state exercise. Interval training works through completely different physiological mechanisms for the potent adaptations from this type of training.
The physiological data on EPOC shows minimal elevations in caloric expenditure.
The 'feeling' post exhaustive exercise is probably associated with other physiological mechanisms, i.e. hormonal stimulation, parasympathetic/sympathetic alterations.
Interesting area of physiology (EPOC), but one that gets beaten up far too much on these boards.
Happy training (and posting people, too much angst/bullshit/you're wrong nonsense going on lately).