Great question. I don't think the answer has anything to do with exclusive brand agreements. YKK makes virtually the same zipper as the RiRi AquaZip. They call it the YKK Aquaseal and it's been around for several years now…at least 3 years.
I think the real question, is why don't we see more of these waterproof toothed zippers that are significantly better than the urethane coated zips that are so prominent today. These new toothed zippers that seal with rubber between the teeth are much better because they are truly waterproof and they zip up with much less drag, like a normal zipper.
I think eventually these types of zippers will totally take over and the answer to why we don't see more is simply because the industry is really slow to change. More specificially, it seems that:
1) A lot of customers may not understand these are a waterproof zippers, and if they do, they probably don't realize why they are better.
2) YKK and RiRi are likely charging more for these zippers since the volumes are low and it's a new product.
3) People associate the look of a traditional backwards urethane coated zipper with serious outdoor gear.
4) There may be some issues in terms of product availability. Perhaps these zippers do not yet come in a sufficient range of colors, lengths and sizes.
I know Helly Hansen has been using the YKK Aquaseal zips in their top line (Odin) for a few years. Westcomb is using the RiRi ones and Arc'teryx is starting to use these (not sure what brand). In a year or two we'll probably see these in most high end coats. Once the look has been established as 'cool', then costs will drop and these will come on most outdoor apparel. As RiRi/YKK start to make these in smaller gauges then they will take over the lightweight (ie. rain jkt) market too. Right now I don't think you can get them smaller than a #5.