I've always been surprised at how so many shoe shops can exist on the same street when they all pump pretty much the same stuff. Oxfords, brogues and loafers in the their thousands.
Having said that, it is quite a sight to behold. If you've ever seen the Hitch Hiker's Guide to the Galaxy film, do you remember the scene when Arthur Dent is taken through to the "factory floor" where they construct planets custom made?
I think Jermyn Street is like my version of that.