i question some people's thought on whether the us general or icon will hold up under professional use. there are guys that have made a whole career out of medium duty cman friction slides. why, because they take care of them. i have also seen snap-n boxes beat to piss in short order by a neanderthal who can break anvils with a 18 oz. ball pein.
things that are taken care of can last under heavy use. those that aren't don't.
Valid points SK but there are some differences. These are directed at US general, not the icon.
The boxes of yesteryear were not as deep (front to back) as today's boxes, so the amount of tools in each drawer were less, thus the weight would be less in each drawer. Less weight = less stress on the drawers.
The friction slices of old boxes were normally fairly stout, can't say the same about some of the BB slides used in cheaper boxes.
The gauge of metal in some of the old Cman stacks was pretty thick. Combine that with smaller drawers and less weight, they would last longer.
As to your point of folks taking care of their boxes, you are absolutely correct. If cared for, a US general should hold up decently, even for a pro for a while. But a busy mechanic will be opening and closing the drawers a lot more then a DIYer, and from what I have seen in boxes, the top of the line truck brands will take a lot more use and abuse then US general or other similar boxes.
Note, I said top of the line. All the truck brands have sold inferior quality boxes that are no better then other run of the mill boxes out there