Bill,
If you're talking about used rifles I think several factors come to play,supply and demand,the romance thing__the white hunter,trekking through the African bush, etc... I compare it with crazy Winchester lever prices and the cowboy thing.Another value factor would be be the records kept by the British makers,a name,not just some hardware store.
As to new rifles,name recognition trumps.If money wasn't a issue,would you rather show your buddy your new rifle,custom made for you by a famous English maker,or one of equal or even better quality built by Joe Schmo in Drippydic Tennessee. If I could build a rifle equal to one made by Steven,(I can't)I could never get more than a fraction of what SDH can charge.I would starve or go broke as a gun maker, because I'm unknown.