Not to sound like a nerd, one of the def. of "spa" is : a commercial establishment (as a resort) providing facilities devoted especially to health, fitness, weight loss, beauty, and relaxation.
I think that what people are trying to convey, without using the word "spa" as a marketing tool, is that their product is meant to relax or "soothe" by using a specific scent that is meant to relax such as lavender or chamomile, or by saying that the products are made with natural ingredients. I try to use the word as little as possible, and when I do, I try to use it in it's proper place, if that makes any sense!

Sonya