70D silnylon was used for constructing the floor of an early model of a Six Moon Designs tent I purchased a few years ago. Since then, I've not had any further experience with this heavier fabric. My observation at the time was that the 70D fabric seemed somewhat more water resistant than 30D silnylon, but it was just as slippery.
So I guess my advice is that if water resistance is your main concern, you may not need the treatment described in the article. However, before deciding, I'd suggest testing the 70D water resistance (I'll assume the fabric is being used for a shelter floor, since I've never seen it used as a canopy material) by placing the fabric on really wet ground, then sitting on it to see if any water pushes through. If it does, it's probably not going to be water resistant enough for you and you'll likely want to apply the treatment, at least to one side.
On the other hand, if solving the slip problem is your main concern, then you'll almost certainly want to apply the treatment.
Hope this helps...