Why are homes wired using solid wire rather than stranded?
A few reasons:


Stranded wire is more expensive to make.
At a given wire gauge, stranded is going to be larger than solid wire (it's the cross-sectional area of conductor that counts and there are going to be some air gaps between conductors with stranded).  This could make a big difference if you have several cables in a limited space like an electrical box.
The main advantage of stranded is that it's more flexible.  You generally don't need this in home wiring because it's all put in place once and hidden behind walls/floors/ceilings.
When you screw a solid wire into a switch or receptacle, you can tell if it's secure.  I could see individual strands coming loose as you fold wires back into an electrical box.


More information in Wikipedia: http://en.wikipedia.org/wiki/Wire#Solid_versus_stranded