Yes, the reinforced slots are real. It got to the point that people were pulling the sockets out of the system. Since the GPUs got so big, people couldn't see the latch and sometimes it was strong enough to overcome all the pins in the socket. That and cards have reached quite epic sizes. More than doubled the average core count, and increased power consumption by about 50%.
Sapphire 6950 wasn't exactly small...There were certainly some monster HD 6000 cards, ASUS DCUII 6970 comes to mind, triple slot card with two large fans. Red Devil 6970 was a triple fan card. Also the era of dual GPU cards, though the official 6990 was a single, woefully inadequate, blower card. Prior to that companies had made their own 6970 X2 cards, which might have reached triple fan territory...
Vertical mounts are mostly for aesthetics in mid towers, actually pretty bad if the GPU is right up against the side panel. In some small form factor builds, necessary.
Tempered glass is the new common side panel, which is quite a good insulator, so not ideal for keeping things cool, but more scratch resistant than acrylic.