Hmmmm, here is my spin...
First, PROPER cardiovascular exercise for fat loss will cause the body to use oxygen more efficiently, thus leading to more fat cals burned. Also, when you do long duration cardio, your body produces more of the enzymes needed to produce energy aerobically, which will also enhance fat loss. HIIT on the other hand will cause the body to produce more of the enzymes that produce energy anaerobically, allowing you to be more explosive.
Now for the performance benefits. The folks over at Westside Barbell REALLY push for cardiovasular exercise. Louie Simmons is a genius and realized that with alot of the Westside routines, you need a very advanced level of cardiovascular conditioning, a level most people do not have. I believe one of the caveats he puts on whether or not someoolne should do a Westside routine is their cardiovascular level. I have seen a bunch of people here at UPENN do them and none of them do it properly. Most take too much of a rest, only do half routines, or have shit ass form. If you are taking too much rest, you don't have the level of cardio fitness you need. I imagine if they even dropped the weight to a weight they could handle they still wouldn't do it right. the Westside parameters are THE way to do the Westside routines. They have been researched by Westside for years, so your theory that "15 extra seconds of rest won't make a difference" is not valid.
Now that I have stated all of that, let's define Proper Cardiovascular Training. Proper Cardiovascular training is the type of cardiovascualr training that less than 1% of the population actually does. It is where you shave time off of your distance run or whatever on at least a weekly basis. When you get to an intensity to where you cannot progress, you are either ripped as hell, a World Class runner, overtraining, or lazy. It IS NOT the type of cardio you do at Bally's while watching TV, chatting to the chick next to you, reading a magazine, or chatting on your cell phone.