yea, could very well be marketing. my concerns would be, is the coco still holding as much oxygen? are any of the buffers still in the coco or still working? could the coco get too decomposed and start to effect PH in the root zone? idk?
the biggest concern is pests/eggs, molds/fungus, and diseases... if you have had any of those problems in the past, then i would seriously think twice about reusing the coco.
Also, some products like Shooting Powder will ruin the coco when it comes to reusing it, because it is so hard to wash out before the next crop (this is the reason i usually cant reuse mine).
But like you said, the huge benefit of reusing the coco is that your micro colonies have a chance of really building up bigger and stronger. Also, the coco will already be generating humic and other beneficial organic acids from the get go. And you save a ton of doe $$$ if u can keep reusing it!... I have to buy close to a thousand dollars worth at a time
coco is expensive, which is a part of the reason why i stay in 2 gallon pots (2gal. works fine for short crops like mj, but if coco was free and space was unlimited, then i might "pot up" to a 3-5 gal.)
and getting rid of the old coco when your done using it can be a problem of its own.