Why heat soup in a blender?

I think you're misunderstanding the claim slightly. You do not heat an already pureed soup, you puree and heat in one step. You can indeed make a hot soup from cold ingredients using certain high end blenders. The only one I've verified this with is the vita-mix. To do this, you put your ingredients in to the blender, turn it on, and let it run about 5 minutes. The friction from the blades heats the soup while chopping the ingredients. The soup will get piping hot.

Why would you do it? It's easy. It takes about 2 mins to get the soup really smooth, so it's 3 more minutes to get it hot. That's faster than you would be able to do with a stove, although maybe slower than a microwave. Is it more efficient? I don't know, but I doubt the difference in electrical efficiency is really sufficient to drive a choice one way or the other.

In terms of cleaning, you already need to clean the blender because you pureed the soup. There's no additional cleaning to do if you cook it there too, versus additional cleaning for stove or microwave. And the blender is easy to clean as it's one piece; you just add soap and water and turn it on for 30 seconds, then rinse.

Personally, I do not think this is "one of the main selling points". It's a neat trick, and it's useful. However, I think that it's more interesting as an indication of the blenders power. You can use these blenders to make exceptionally smooth soup, make peanut butter, properly crush ice for frozen drinks, etc. They do this much better than a 'normal' home blender, but just saying 'better' probably wouldn't sell a lot of these things at 4x the price, so they focus on something that the standard home blender most certainly cannot do.

There is no doubt that raw ingredients maintain more vitamins. Is it a big deal to me? not really. The soup in vitamix never boils or simmers, or anything really close. So it is virtually raw.

however, that means the uses are limited. If you want a rich-tasting soup, that's usually going to mean caramelizing your onions and garlic a little, slow-simmering the carrots to bring out their sweetness. I have the Vitamix 5200 and love it but the soup-making feature is so far not one that I care for. My brother-in-law supposedly invents all kinds of great, nearly instant soups in it; when he's a little less busy (he and my sister are moving), I hope to get some advice from him.

So far, the soups I've made, even following the recipe exactly, are not great soups. The onion and garlic give it a very sharp taste with no actual cooking, the whole soup tastes sharp and off instead of rich and warming. I wish I had gotten the cheaper version that does the same stuff but without the automatic timers. Not a big deal.

The main thing ot love about the Vitamix i that it is a powerful and sturdy machine. I'm tired of $50 blenders that conk out after a half a year. Now, truly, I like a thick smoothie. Really thick. But on my last blender, it was the "on" button that broke. How weird is that?

The Vitamix is guaranteed for seven years. no questions. I bring it back to Costco, they replace it if it breaks. Meanwhile, what I can make in my Vitamix that I can't do in the other blenders is an awesome no-sugar-added sorbet, and I do that several times a week. I also made pistachio butter, which is probably too good to be legal.

This is a prime example of taking something that is a negative about a product and spinning it to a selling point. "It's not a bug, it's a feature!"

An ideal blender would not impact the temperature of the contents. Physics intrudes, friction and waste heat affect the contents of any blender. This company chooses to amp it up.

From an energy efficiency standpoint it is also a very wasteful path to move potential into heated soup.

@Blrfl I was thinking the same thing (well, I haven't looked at the wattages on my microwave or converted things on my gas stove. BUT, the fact that you will almost certainly be heating less water to clean the blender than the additional dishes does factor in on the energy efficiency side of things. As a selling point, it is also just a way of eliminating extra steps. My wife and I just got one of these upscale blenders (a Vitamix) and I will often preheat a cup or two of water and then the blender heats the remainder of the ingredients the rest of the way. I'd argue that in general you aren't truly cooking most of the ingredients. Rather, you are pulverizing them and warming them to a low heat over a few minutes (considerably less than the near sustained boiling temps of a normal soup would require). On the flip side, the pulverizing does increase the surface area of the ingredients considerably, so they tend to warm up very quickly. Overall, these blenders basically advertise "meal in a blender in 10 minutes" and for things like soups, that does seem to ring true. For cleaning, I find for most things I still have to do a bit of handwashing, but not that much....YMMV.

In short, use it the way that makes you happy. It has reversing features so while the food is spinning in one direction, you can reverse the motor so the blades impact the fast moving mixture in reverse creating a lot of friction this consistent action surprisingly heats the soup perfectly, especially with broccoli and cheese. The texture is is perfection and unlike stovetop cooking, the cheese doesn't settle and stick to the bottom. And according to my nutritionist, more nutrients and enzymes are maintained by this method.