Kcscott hit the nail on the head, in the case of most horses. Also, that's a great article!
Just for the other side of things (so the blanketing "argument" is balanced, pro/con), I blanket my mare because she's older, Also, even though the area we live in is pretty temperate, she'll just stand in her shelter all day which isn't great for preventing arthritis. I choose to blanket her because, even though she would survive without it, she's obviously more comfortable with her blanket on.
She's also MUCH more active with a blanket on. If she's a little cold, she'll generally just walk slowly around the pasture but if she's warm enough, she'll be galloping and bucking around. Since active=healthy, there's reason #million that I blanket her.
Another benefit, for me, is that my mare seems to get cold really easily (I'm sure it's age related) so she eats a TON when she's not blanketed and the littlest bit cold (hay helps horses stay warm). As I'm a college student, I don't have the money to be buying tons of hay all the time so blanketing helps me save my money for more important things, like vet bills!
I also hate saddling a wet horse (another thing the horse would definitely survive that I just feel bad about) so, being that we live in Oregon, blanketing is necessary to prevent wet-horse-saddling. In your case, since they're mini's, I hope you aren't saddling them. Haha!
Sweaty horses can be a problem but if you follow a blanketing chart pretty closely and/or clip your horses, you shouldn't have a problem. The only time I've had issues is when I only had a medium weight blanket and it was 50 degrees F. She got a little sweaty then but I took the blanket off as soon as I noticed and she was fine and happy again.
For my mare, I've noticed that keeping her warm enough is more of a problem that keeping her from getting too hot, however, I feel like my mare is the weirdo on the blanketing block because she's gentle on blankets, never sweats in them, etc.
All that being said, if your horses have enough hay and shelter to access and they aren't clipped, it might be in their best interest to be unblanketed. But they could also be just as happy being blanketed. You know all the factors happening for you so calculate the best method for your life/your horses' lives. :)