I am not sure I follow the argument; you called the brick and mortar stores "valuable", but selling direct also leads to their death
It's questionable to me that selling direct would provide the same level of service and product exposure that a dealer of any kind adds, including online stores, and would increase consumer dependence on hear-say and reviews, and limit overall exposure to the plethora of products available. Online stores can still sometimes offer very good advice, more generous returns and longer home-audition periods, set-up help (they set up my VPI table's arm for free, and it was correct when I checked it), they interface with vendors that are hard to get on the phone like VPI, occasionally offer convenient payments with 0% interest for X months, and more. What you don't get is the personal touch, the lengthy discussions that a local dealer is able to provide, in-home consultations, of course in-store demos, and breadth of knowledge - by contrast online stores will often offer a dry, shallow "try it and see how you like it", and for things like cartridges this is not even an option, because there is usually no return policy (just high trade-in value) - I bought my A90 from MusicDirect based purely on my own technical analysis, so slightly better than a shot in the dark; however, they did offer the highest trade-in value for my XX-2.
The bottom line is, if an online dealer overall cannot exactly offer the same level of service a local brick and mortar store will, I can't see how selling direct would even approach either.
Having said that, overall, I have probably spent 70% of my budget locally...