Complicated question. Whole books are written on distribution strategy (and this is an area of professional expertise for me, but not in the audio business).
Manufacturers want lots is sales, and generally think this means lots of dealers. However, they want dealers who will represent their products well, including demonstrating them, and normally this means the dealer must buy demo equipment, which can be very costly. Therefore, convincing a dealer to carry your product if you are someone other than B&W or Harmon can be difficult.
But even B&W is careful to get dealers who will do a good job because this effects the customer experience. I have bought much of my audio gear in the last 10 years online (before that there WAS no online
). But I bought my big B&W's from a local dealer because I wanted the support that comes with it. For no cost other than the (admittedly substantial) cost of the speakers, the dealer delivered them, and helped me "dial them in". If I had ever had a problem (which I have not), they would have immediately come to my house to fix it. No extra charge. Try getting that from a website.
And yes, dealers will most actively promote products they make the most money on. They SHOULD - they are a BUSINESS. That said, most hi-end stores don't discount too much, and margins are generally very similar for hi-fi gear (dealer gross margins are 20-30%).
It is unethical, IMO, to go to a dealer, demo a product, and then buy it online. You are using a dealer's valuable time, and he should be compensated for that. As such, many dealers do avoid manufacturers who sell online, for that very reason. Again, an audio dealership is a business, and needs to make money to be a business.
Here is the other key "hidden" fact - buy ONE fairly pricey item from an audio dealer, and they will love you long time
After buying my speakers from a local dealer, that dealer will let me borrow for a free home audition any piece of equipment they have in the store. No problem. And they greet me with a smile when I walk in!