Olivier remember there are no dummy questions, there are just, as one of my former teachers usually said, dumb answers....
As far as the press is concerned, it is exactly as you say. When I was doing the design I found out that the lower part of the press (the tripled I beam) is displaced for nearly 2/10ths of a mm when the hydraulics is fully engaged to 25tons. Well that was too much for me, and the I-beam was already 340mm (!) with doublers at top and bottom. Then I decided to design the upper parts so that they deform the same way to still keep the bending operation very precise. That way I could save some money on the material (1kg steel is about 1€ at the moment as far as I know) and keep the press mobile and light (check the wheels).
About you comment concerning the presed parts:
I think we are not talking about the same things here:
Lets consider parts curved in two directions (like e.g. a roof) and parts pressed like e.g. ribs, floor panels and so on which are structurally important.
The main thought about a monocoque is that you use thin walled and closed cells like e.g. the sponsons of the racecars of the 60s or, the classic, the fuselage or wing of an aircraft. These configurations produce very stiff and effective structures (both in bending and torsion) mechanically. Structures loaded purely in tension don't need to be hollow, just if loaded in compression and in danger of buckling (which is - in the end something like bending, for example).
So there are two ways of designing lightweight and effective things (here: car structures):
do them membrane like (with closed, thinwalled cells) or with members just loaded in tension and compression. First being the 'monocoque' (exactly said it would be a multihull or something like that term) and the latter one the frame structure (compare e.g. the Maserati Birdcage).
Both types can be brought to about the same performance in my opinion and experience, but each type has it pros and cons.
Now about the pressed parts: using them doesn't give you huge benefits in terms of lightweight design. It makes it easier to do the joints, mounts and everything else. But this just makes sense if you intend to produce a high number of parts, not just a prototype and a few more.
Just look at the finest of the lightweight designs: the airplane. Here we have completely hollow structures with ribs or bulkheads on the inside to prevent buckling (which is dangerous if the walls get thinner and thinner in design). There are not many pressed parts there, just some ribs or the pressure dome at the end of the cabin (and this has other reasons). Automobile industry just likes the forming of sheets because this can be done quite well in the series and the curved shape of a cars body can be made in that way quite easily.
Using composites doesn't change anything on these principles. This material however is something that the designer has to use very carefully because it has no means of ductility AND possesses directional stiffnes and strength. All the points where loads are introduced have to be designed very carefully and with mechanical understandig. But apart from that the composite material is 'just' another material which has good specific stiffness and strength (and, as well cost...).
