What James says is true about the radius of connection. However, two things have been driving that radius smaller - smaller gate size and chip stacking. We all recognize that making the transistors and the gates smaller decreases this radius, but what is not widely recognized is chip stacking technology is becoming more common. The issue with chip stacking is the heat dissipation. This was addressed by IBM, for example, using liquid cooled systems and stacking years ago. However, once the IC power is reduced, chip stacking becomes very practical. It is currently used to stack memories on top of processors in a lot of consumer devices.
Going up provides a lot of opportunity for increased performance by adding complexity without substantially increasing the radius of connection. There is presently a lot of headroom in this technology for additional Moore's law advance.
