iternabe Are those pianos reinforced, or stock? I can see the top plate of upright bend under Fred‘s weight. That thin lid support of the grand’s seems impressively strong.
I strongly suspect that the lid and prop of the grand were reinforced. In some shots you can see that there is also an extra support for the lid, approximately in the middle. Probably the strings had been removed and the pianist was miming: there are moments where Fred is dancing more or less where the dampers should be, and we hear taps, as if the strings had been replaced with a solid plank. This would also have left enough room to put in a special compartment for the cats.
The upright might well have been unaltered. The action is working, Fred seems to be really playing (he was a proficient pianist), and most uprights are built to withstand heavy use. As a kid I got up on top of our upright piano and I can assure you it wasn't any the worse for it, whatever my parents might have said to the contrary.
iternabe Another question, do pianists baby their intrument? For amateurs who own expensive piano they love at home, I can see why. But what about pros?
I'm a pro and I take great care of my piano. Certainly the most important things are tuning and regulation, but I also dust it regularly and make sure that it doesn't get scratched. The cat isn't allowed in the piano room!