Hi Bee159,
With Ecommerce, it is all about the user experience. Detail the products so the consumer knows exactly what they are buying. Even the simplest of products can benefit from a detailed description. I do not know how many times I am shopping for a product and there are many brands of the same item. What it is going to set it apart? A good description.
So its not word count... it is more like "Words Have Meaning" give value to your descriptions and more people will choose your products over the competitors.