What does a Single Dealer Platform have in common with Bond Street in London?

[Note for non-UK readers, Bond Street is an upmarket shopping street in the West End of London.  Pretty much every upmarket retailer globally has a shop on Bond Street - Cartier, Ralph Lauren, Chanel, Louis Vuitton, Bregeut and so on]

So why is a single dealer platform in any way, shape or form similar?  Simple.  It's a shop window.
If you ever walk down Bond Street very early, say 5am, you will see teams of people cleaning up the pavements, clearing rubbish, cleaning windows, polishing door handles.  All before the shops open.
Look at any investment bank, before the market opens in their time zone they will have an early shift running start of day processes, checking that static data updates have been loaded, that the pricing engines are reporting connectivity to their data sources, the webservers are up, the middleware is running and so on.
What happens during the trading day? 
For the retailers, they receive customers through the front door who buy whatever fancy trinket that takes their fancy.  A customer buying any item will be treated with courtesy and respect.  But certain larger customers will be discretely escorted to a private room and shown items that may not be available to the general public.
For an investment bank the SDP publishes out prices which show market participants that they are involved in a particular currency pair or instrument.  When a big client wants to trade they may well find that they receive a telephone call from their sales coverage person within the bank to see if the bank can assist.
The point is that the SDP can provide scale at a sensible price - to allow small customers to self serve, to allow larger customers to indicate interest and then receive targeted interaction from the sales force.
And in the same way that retailers will offer to deliver the shopping all nicely wrapped up to the client's home, the bank can use FIX to ensure that there is "straight-through-processing" - the equivalent of delivery to the customer.
And again, think of the way that retailers offer multiple channels - "clicks-and-mortar".  The typical SDP needs to offer a holistically integrated experience - web-browser, mobile device and the human touch when needed.