Yes, I have to think that BN holds a majority of the market share for a brand like Slumberhouse, for example. Certainly not for the bigger, commercial houses, however.
May be actually possible. The purchasing power, but also the quantity and quality of fragrance purchases of some, if not most Basenoters may start influencing the turnovers of fragrance market, at least marginally and possibly in the long-run. Perhaps not the best-selling designer houses, though most Basenotes members are regular customers of these too, yet even their most extensive fragrance buys likely go unnoticed among their giant turnovers.
On the other hand, I do believe in the niche theory, so that especially small niche companies may be interested and even benefiting from what happens on Basenotes, since these companies cannot fully rely on the mass-market alone to ensure their turnover.
So there is a quite strong case in favor of this theory.
It would be good to post them somewhere. I know about them but always forget when it comes to actually ordering anything.
I doubt the overall purchases of members here make that much of a difference, altho some of the more artisanal houses might benefit from a ripple of interest in a particular release. I certainly hope profumo.it has seen some action from members for masterpieces like Mecca Balsam, and that more intrepid members have tracked down some of the cutting edge 'owner operated' stuff that gets mentioned.
That said, the collective voice of basenotes can help to give a brand or a specific release traction and the companies know it. Obviously Creed play up the young crowd discovering 'niche' for the first time, which is why you can be sure of an Aventus or whatever thread always being on the front page - and the recent influx of tweens is a perfect demographic for them.
Ultimately I think basenotes is a handy place for companies to have new releases discussed but if it was really influential you would see it in the adspend allocated in this direction and I don't see a lot of that . . . the more influential blogs seem to be picking up more revenue from advertisers these days.