Drvrage, not to speak for Henry (God forbid!) but an awful lot has changed between "old" SxS's and their modern counterparts - some for the good, some not.
The heart of any good SxS is the barrels. In older guns, SxS barrels are carefully struck thin walled tubes of chopper lump or dovetail lump construction. In newer guns, such as the Ringneck pictured above, the tubes are thick(er) walled and belled at the muzzle to accommodate removable choke tubes. They are also of monobloc(k) construction. All of this affects the balance of the gun. The centre of balance of the barrel assembly is now farther forward, giving the whole gun a higher polar moment of inertia.
Building barrels the "old" way is more labour intensive and therefore expensive. It does, however, give better handling. Many new guns are built with chopper lump barrels, but their price now takes them out of the mass market. Older guns such as a Webley & Scott give you the inherent superior balance without the price tag. The trade off is in ammunition - no steel shot capabilities and short chambers mean you cannot just waltz down to CanTire for all your ammo needs.
There are differences in the frames and locks as well, even if we restrict ourselves to boxlocks. Metal thickness, polishing, hand fitting, the type of springs used and their construction, and niceties such as bushed firing pins come to mind. For instance the Ringneck uses mousetrap style springs to power the sears, vs. V springs which provide a crisper feel.
Fit and finish, while certainly acceptable in modern guns, usually cannot compete with an older gun made by hand. There are many exceptions of course, and a cheap gun was always just a cheap gun.
The bottom line is that for around the price of a new Ringneck one can find examples of older boxlocks that are superior in balance and handling, and fit and finish when compared to guns of newer construction. What you give up is modern ammo compatibility, warranty and availability (you have to hunt for such guns). Would I council someone to look for such a gun for their first SxS? No. For their second, yes.
For the dedicated SxS shooter, balance and handling are of primary importance. The search for the gun and the ammo to feed it is worth the effort.
Don't get me wrong, I own and shoot modern SxS's and have a Bobwhite (cousin to the Ringneck) that I like. None of them have the feel and handling of an old Army & Navy boxlock non-ejector from the early 1920's, though. There is much more to it than price, exclusivity and general snobishness.
Sharptail