You are getting into an area of greyness when you are looking at more high end gear like this.
You see, do you really get all the value out of B&W speakers vs. Paradigm or others vs. spending a good deal less on other brands? Is spending three to five times the price of a standard DVD/CD player going to deliver anything more for you? Especially compared to DVD-A or SACD? I've seen people who have spent thousands of dollars on analog gear just to replace it with a $100 DVD player and be just as happy.
Where you fit into this mix is not something anyone can decide other than you. There is a line between cost and quality that everyone needs to hit. Does biwiring make sense? Not really - but extra wire to carry more power is rarely bad. Does bi-AMPING make sense? Absolutely! If done correctly it can be a very good improvement to a high end system.
On high-end setups I always run 2 pairs of wiring to all speaker locations - but it is for future bi-amping, not biwiring capabilities.
Now, how does this all come back to the shop?
1. This guy likes music. From your own writing it is easy to tell that this guy simply enjoys audio. He isn't pressuring you and if he owns the store he makes his LIVING off of what he sells you. But, he didn't pressure you or anything. So, he's a firm believer that what he sells is good enough to sell itself.
2. He doesn't just like music - he loves it. It is his passion - his religion. As with most religions there are certain aspects that some may glom onto that may simply be untrue. Pure myth. If you don't share that belief in religion then you may not buy into the myth. It's important to note that you have the option of asking him not to push that myth onto you as you've done your homework to show that it isn't true. Or you can just let it slide that his myth doesn't have to be your myth but he can still have his.
3. The cost of cabling is nothing. Twenty or thirty bucks for cable after spending hundreds - or thousands - on near full MSRP product is a nice bonus but doesn't even equate to 5% of the sales price. If you aren't being a douche about the price of the gear he is selling - and are willing to pay at or near full MSRP, then this retailer is saying "Thanks for not being a jerk" by automatically including some freebies that he thinks you will value. That's a win-win! You see, he likely pays $.50 a foot so it is far less out of his pocket to give those cables to you than to discount the price... Plus, you get something that is good for your setup. You both are happy!
4. Talking you down, very mildly, on other product... This is better than most do. He didn't act to condesending or anything. I'm of the belief that there are about 10,000 top notch speaker companies out there that provide a good product for the money you spend. Only a few companies are really a lousy value. So, he can't possibly affect your sale in a good way by talking down the competition. You have to decide for yourself what you like or dislike and he has to accept it. He clearly knows this and lives with it. Thumbs up on the attitude. Even people here are going into different factors about the speakers that are differences in design/build... But - how do they sound to you? And at what cost to you for that sound? Drivers in boxes... they ARE all really the same... so go find what you like.
5. B&W is B&W... Their boxes are known for quality as are their drivers... and you pay for it. A bit more than typical. Yet, I've gotta say that if I had the money availlable I would be hard pressed not to pick up at least one setup of B&Ws. They are gorgeous and sound great. They DO sell themselves.
Just my opinion but it seems like you found a rare gem in the A/V industry that may prove valuable to your future endeavors. If you don't abuse it, then you may find yourself very happy in the long run. On the other hand, you could ditch the brick & mortar altogether and go online, decide for yourself, and save a fair bit of cash for your own extra efforts.
