Most large American stations worked this way even during the heyday of their railways, consequently all the architectural grandeur was in the main hall and the platforms were usually pretty squalid by comparison. Grand Central is probably the most obvious example but others like Chicago Union and Los Angeles Union still have a very impressive waiting hall but very undistinguished platforms.
However, from the pictures I've seen the old Penn station seems to have been an exception to this, being more on the European model with at least part of the platforms being relatively open and visible, vaguely reminiscent of Liverpool Street in fact.
It may well be that airport terminals copied the lounge-and-gate model from American railway stations.
Chicago Union is made all the more bizarre by retaining its original (and rather wonderful) old building as a waiting room, and having you walk through a tunnel under the road to the new, impressively confusing station.
Confusing? Yes, because, although there are through lines, the platforms are all bays facing north or south. The north-facing platforms are odd-numbered and the south-facing platforms are even-numbered. There's a cramped rabbit warren of shops and check-in desks between and above them, in an undistinguished modernish style (there's also street access to this building).
In common with most major US stations, the platforms are industrial concrete afterthoughts, reminiscent mostly of unloved underground shopping centre loading bays. If you're lucky enough to travel on Amtrak first class, you do have a lounge, and get paraded out to the train through an odd back route across a barrow crossing.
Chicago does have a lot of terminus stations - unconnected and in odd locations. Perhaps the oddest is the South Shore Line section of the Millennium Station, which is literally hidden away in an underground car park, accessible via the odd series of underground walkways designed for the harsh winters.
Some of the stations along this line are quite wonderful - barely used urban halts made almost entirely of wood.