UPDATE March 10, 2012. Based upon new information forwarded to me, I am deleting some of this message. My revised opinions will appear after the messages of March 9, 2012. I am just leaving my recollections of the RD in Queens, NY in this message.
My opinion for the "Not Open to the Public" stance? Zoning laws and finagles, sales and income tax issues, cost reduction by keeping out the people who don't know how to behave in warehouses.
I didn't know it for a long time, but I was a customer of the very first Restaurant Depot, going back to about 1992. A few blocks from where my sister lives was a foodservice distributor by the name of Hyco Restaurant Supply Company. Exact address was 54-44 74th Street in Elmhurst (Queens), NY 11373. You used to see Hyco delivery trucks in front of places serving food all over Queens. Even back then, I knew that there was good 'eatin to be had from foodservice cash & carry outlets. My sister told me about the fact that this was a cash & carry. FundingUniverse.com gives the opening of RD as 1990. I would not be surprised if the founders ripped off the Staples (founded 1985) concept. From here on in, I am relying on memory and some of the things I may not get right. But I think it gives a general explanation for their rationale.
Back about 1990, guys like Sysco were getting bigger and guys like Hyco were facing stiff competition. Foodservice guys were also charging big bucks to deliver food to mom-and-pops. Hyco let people walk around their existing warehouse and put things on wagons, just like at Home Depot. You just walked in, like at K-Mart. There was no trade credit; you had to pay by credit cards or cash. There was also no delivery included at that price. But the prices were low. To my eye, many of the people in cook's whites buying food for their bosses were illegals. On weekends, you would find people in there who obviously did not work in restaurants.
Sometime in the 90's, they started offering "membership cards", with a discount for using them. I also seem to recall the prices going up overnight by the same amount as you could save by using the card. Then, they started making you either have a membership card or a "temporary pass" in order to check out. You could still sneak in the door, however. The obvious "cooking enthusiasts" would simply ask the pretty girls at the desk for a temporary pass. A while later, they made you sign a swindle sheet to get the temporary pass. No ID required, probably because they knew most of the green cards were phony anyway. They did charge sales tax on non-foods on those temporary passes, though food in NY City is untaxed.
Restaurant Depot started to expand in the Metro NYC area. They would go into areas zoned for industrial use. I am really fuzzy on this, but I think I remember some resistance in one place, with opponents claiming this was a retail application rather than a industrial application. At the new locations, you had to have a good cock-and-bull story to get them to sell to you without a business license. After reading the Fundinguniverse history, I think it may have also been because the owner of RD since 1994, Jetro, also ran a wholesale cash & carry grocery operation catering to mom-and-pop groceries and bodegas. Jetro sells the likes of cases of small cans of Campbell's Condensed Cream of Mushroom soup.
As for Hyco Restaurant Supply Company, they too are now owned by Jetro and operate out of a warehouse in the Bronx:http://hyco-restaurant-supply.com
If you put the address of Hyco into Google Maps and go for the street views, you will get images from 2007 showing the first RD location vacant and before being sold to a self-storage facility operator. The customer entrance and customer parking lot was around the corner on 57th Avenue; just click on the arrows to waltz around the corner. RD Elmhurst moved to a larger building in nearby Maspeth, NY.