I am aware that USB uses a positive, negative and D+/- wires in order to transmit data. The twisted pair are used to negate the effects of interference and electronic noise.
I also understand that a cable needs to be thick enough to carry the necessary current, and connections need to be made properly so that high frequency signals are not reflected etc. Based on my limited knowledge I believe this is due to AC impedance being proportional to frequency.
However, presuming a high enough quality cable, and a fast enough chipset to handle the data, is there any reason why we cannot connect all common devices over such a 4-cable system? (Ignoring the user experience)? Could PCI-E and all other digital serial interfaces be replaced by a fast enough USB like system? If not, why?