The difference in price between the best Cat-x UTP and the lowest rated bell wire is negligible when compared with the labor to install it. You should always be pulling cat5e or better (whatever the state of the art is) and that will be plenty for residential networking for the foreseeable future. We were talking about the death of copper in the late 80s but if anything, the technology is moving in the direction of shoving more data down wire.
I do think any responsible builder should be wiring houses for networks but I also think this is a design issue, not a code issue.
