A traditional window is almost always built with mortise and tenon joinery. The visible result of this is "joinery lines" that are a continuation of the stiles (vertical sash members). These joints are not meant to be decorative but regardless of the quality of construction will be visible at all four corners of the sash where the parts come together. Many historical oversight entities disallow clad windows, partially due to the prevalence of "mitered corners" in this type of construction (see below). The Magnum's Joinery Lines perfectly follow the stiles and it's impossible to tell, even upon close inspection, that the exterior is not wood.
See also gad example below. Meeting rail is the same size as the stile and the joint is horizontal rather than vertical as in most historic windows.
Almost invariably, double-hung meeting rails are 1.25" tall. Likewise, stiles are typically 2.25" wide, less the 1/2" parting stop that holds them in place leaves a 1.75" reveal. Does this meeting rail look thinner than the stile? That's the problem with most replacement windows, a disregard for the ratios evidenced in traditional window systems, which results in a loss of character. Note also meeting rail joint is horizontal vs vertical.
While there is no absolute standard regarding stile and rail sizes, The bottom rails of a traditional double-hung window are almost always an inch or so wider than the stiles and the stiles are around a 3/8" - 5/8" wider than the meeting rails and the meeting rails ALWAYS line up. Despite these seemingly small differences, the overall effect is noticeable. All the details mentioned on this page add up to something significant - HISTORIC CHARACTER. Either it's maintained or lost.