My house was built in the 80s. I am not aware of any special materials, but the pipes and wiring in the wall more or less kill all cell signal if you aren't on the side of the house facing the tower (I forget the term for it, but I have the kind of baseboard heaters that use hot water). And considering a lot of other houses in the neighborhood have the same issue, it rapidly becomes one or two rooms where I have cell reception. Actually means I bother to set up a guest network on my wifi so that people who come over that I don't trust to have access to my personal network can still receive texts and the like.

In terms of wifi? If I put the wireless access point in the living room, I more or less have signal. But my drop is in the basement (which is awesome for my server room needs) and that means upstairs has a LOT of dead zones.

It really depends on construction, but this is WHY office buildings are designed around this. I just don't think apartment complexes need to be because you are going to have an ethernet drop in every unit anyway.