Moores Law states "The number of transistors that can be inexpensively placed on an integrated circuit is increasing exponentially, doubling approximately every two years"
A consequence of this has been that for a very long time (in computer terms) we have seen an approximate doubling of processing power on a processor with a slight reduction in cost and energy use every 18 months; there are time periods where the focus has been on increasing processing power faster than that which has resulted in faster, more expensive and higher energy use processors.
If you assume that the PS4 will be released 6 years after the PS3 was, it shouldn't be all that difficult to produce a system which is (roughly) 6 to 8 times as powerful as the PS3 in an affordable and low energy use compared to the launch PS3 systems.
