Hi George
The difference is amazingly large. Anyone can set up a Retail website (on eBay or Amazon for example) in an hour. True, it won't like to Adagio, but for small volumes and small item lists, that's not a big deal. But even linking to Adagio isn't that big a deal.
With B2B, trade credit is one issue. The major issue though, is presenting the correct price for a customer, which can be a complicated issue, what with sales prices, customer discounts, quantity breaks, special prices and alternative price lists. All of this information, as well as credit limits, etc, must be passed back and forth between Adagio and the website. And I'm sure there's a lot more I haven't thought about.
Steve